1955 MacArthur Airport United Airlines crash
Encyclopedia
On April 4, 1955, a United Airlines
Douglas DC-6
named Mainliner Idaho crashed shortly after taking off from Long Island MacArthur Airport
, in Ronkonkoma
, Islip
, New York
, United States
. The aircraft, registration number
N37512, was performing an instrument rating
check flight, when, shortly after taking off, it began banking to the right. Seconds after climbing through 150 feet (45.7 m), the aircraft turned through 90 degrees, causing the nose to drop suddenly, before it impacted with the ground.
A subsequent investigation found that the flight crew were simulating an engine failure, which involved a member of the crew pulling back the throttle
lever for engine No.
4 prior to taking off. Investigators found that if the throttle lever was pulled back too far, however, it would cause the propeller to reverse
—a feature designed to slow the aircraft
upon landing. Once the landing gear was raised, the crew would have to raise a metal flag in the cockpit to bring the propeller blades back into the correct position, since a safety device prevented electric power from operating the rotating mechanism at the roots of the blades unless the aircraft was on the ground or the flag was manually raised. Investigators from the Civil Aeronautics Board (CAB) concluded that one of the flight crew applied full power to No. 4 engine, thinking this would bring the aircraft out of the increasing bank. But because the blades were reversed and the flag was not raised, the dramatically increased reverse thrust caused the DC-6 to spiral out of control. The investigators also concluded that the suddenness of the bank and dive meant the flight crew had little chance to recover the aircraft before impact.
In the aftermath of the accident, the Civil Aeronautics Administration (CAA) issued an Airworthiness Directive
ordering all DC-6 and DC-6B aircraft be fitted with a manual device which could prevent the inadvertent reversal of the propeller blades. United Airlines also stated they had begun installing reverse thrust indicator lights in the cockpits of their DC-6 aircraft, which would warn pilots when a propeller had reversed.
checks on two of the airline's pilots. Hoyt had been employed by United Airlines in 1937, and had 9,763 flying hours experience, 549 of which were in a DC-6. He was training the two pilots, Henry M. Dozier, age 40, and Vernis H. Webb, age 35, so they would be able to retain an instrument rating qualification, allowing them to fly under instrument flight rules
. The aircraft was a Douglas DC-6
, registration
N37512, serial number
43001. The airframe had flown 22,068 flying hours, and had undergone an inspection 105 hours before the accident. The aircraft was powered by four Pratt & Whitney
R2800-CB16
engines, fitted with Hamilton Standard
43E60-317 propellers.
The weather on the day of the accident was clear, although there was a strong wind of about 20 knots hitting the airfield from the southwest, with occasional gusts of wind as fast as 30 knots. The aircraft made several circuits, taking off and landing again, before eyewitnesses observed the aircraft standing at the end of the runway
and then taking off at about 15:50 Eastern Standard Time
. Loaded with around 61000 pounds (27,669.1 kg), the aircraft was far below its maximum permissible weight and the center of gravity
was within the prescribed limits for the model of aircraft.
Between 1500 feet (457.2 m) and 1800 feet (548.6 m) down the runway, the aircraft reached take-off speed
, lifted off the ground, and began climbing normally as the crew retracted the landing gear
. Upon climbing through 50 feet (15.2 m), however, the aircraft began banking
right. The climbing bank continued to increase at a rate which alarmed witnesses, and soon after the aircraft rotated through 90°
(at which point the wings were vertical to the ground). At a height of around 150 feet (45.7 m), with all four engines producing take-off thrust
, the nose began to fall, and the aircraft stalled
. The right wing and nose impacted with the ground, causing the fuselage to cartwheel over, before the aircraft came to rest the correct side up and was engulfed in flames. Though emergency services at Long Island MacArthur responded to the crash, all three members of the flight crew had been killed on impact. The aircraft was destroyed by the post-crash fire.
Investigators were also able to determine all of the flight control surfaces, including the elevators
, aileron
s and rudder
, were functioning correctly at the point of the crash, and it was also found there were no faults in the flight control system of the aircraft. The flaps
, it was found, were extended to between 15° and 20°, the standard setting for take-off. Investigators did discover, however, that the propeller blades of No. 4 engine—the engine on the far right side of the aircraft—were reversed. While the blades of Nos. 1, 2 and 3 engines were at 34° positive pitch
(also standard for take-off), the blades of No. 4 engine were set at full reverse pitch—minus 8°.
when the aircraft touches down. When this feature is activated, the propellers begin producing thrust in the opposite direction, propelling the aircraft backwards to slow it down. When the crew then retards the throttle levers, electric mechanisms in the propeller hub rotate the blades
to a position in which they will provide reverse thrust. Should a crew need to perform a go-around
, they could restore the thrust levers to a positive position and again produce forward thrust, allowing them to execute the maneuver.
The Douglas Aircraft Company
, however, designed a system that would prevent the accidental reversal of propeller blades in-flight. During development of the DC-6, the company installed a system that cut electrical power to the mechanisms which rotated the blades while the airplane was in the air. When there was enough weight on the landing gear
(which would only be the case when the aircraft was on the ground), a switch which supplied electrical power to the mechanisms was closed—meaning that when the aircraft touched down the blades could be reversed and thus the airplane could be slowed. When the switch was closed, a red flag would swing into view in the cockpit of the aircraft, warning the crew that the blades could be reversed. Should the switch fail to close upon landing, the flag could be raised manually and electrical power to the mechanisms would be restored. When the aircraft took off, electrical power would be cut to the mechanisms so that the propeller blades could not be inadvertently reversed, and the red flag swung out of sight. Reverse thrust warning lamps, which would have warned the crew if the propellers were reversed, were not fitted on Mainliner Idaho.
If full left aileron
was applied, the aircraft could be recovered for a short period of time, but a violent turn to the right would continue, and the competing forces would cause the aircraft to stall
, and violently roll and pitch down. Flight tests, investigators said, accurately reproduced what happened to Mainliner Idaho during the accident sequence. The tests performed by United and by the investigators showed that if, after the aircraft became airborne, full power was applied to an engine whose propellers were reversed, the propellers would produce not positive thrust, but increased reverse thrust. One aviation author wrote of the crash,
The investigation concluded that the accident sequence began when the check pilot, while the aircraft was on the ground, retarded the throttle lever for No. 4 engine past the idle position, and therefore reversed the propellers of the aircraft. Once the airplane took off and started banking to the right, it would have been a natural reaction for one of the flight crew to increase power to No. 4 engine, thinking that by doing so the engine would start producing positive thrust and the aircraft could be recovered. However, since the metal flag was not raised, there was no electrical power to the rotating mechanisms—and increasing power to No. 4 engine would only have created more reverse thrust.
The final accident report concluded that there was no time for the crew to react, since the dive began so suddenly, and there was no way for the crew to recover the aircraft. "Control will be lost so quickly that there is little, if anything, that the pilot can do if it occurs at low altitude," the report stated. "He must recognize what is occurring, analyze it, and take action to unreverse in a very limited amount of time. It is doubtful that unreversing could have been accomplished in this instance before control was lost." On October 4, 1955, the CAB released the final accident report, which concluded the reversal of the propellers and subsequent increase in power to No. 4 engine had caused the accident.
ordering all DC-6 and DC-6B aircraft to be fitted with a sequence gate latch, known as a Martin bar. The device is a metal bar which a crew would manually swing in front of the thrust levers over the idle line, physically preventing the thrust levers from being retarded into the reverse position. According to the CAB report, a United Airlines engineer told investigators the Martin bar should make propeller reversal "a more reliable and safer device [than the system fitted to Mainliner Idaho] ... with its numerous switches, relays, and automatic operation."
United Airlines issued a statement saying it had begun installing the device on its fleet of DC-6 and DC-6B aircraft one week before the accident, having used it successfully in service on their fleet of Douglas DC-7
aircraft. A Martin bar had not yet been fitted on Mainliner Idaho. United Airlines also said a program had begun to install reverse thrust indicator lights on all their DC-6 and DC-6B aircraft. The signals, fitted in the cockpit of the aircraft, would have warned the flight crew that the thrust lever had been pulled back too far, and the propellers had been reversed.
operating United Airlines Flight 859
crashed in 1961 when the first officer attempted to reverse all four engines during the landing roll. The left engines remained in forward thrust, while the right engines went into reverse, causing the aircraft to veer rapidly to the right and collide with airport construction vehicles, killing 18 of the 122 people aboard.
Japan Airlines Flight 350
, a DC-8, crashed in 1982 short of the runway in Tokyo
, after the mentally ill captain attempted suicide during the final approach phase of the flight, by putting the inboard engines into reverse thrust. Of the 174 people aboard, 24 died.
In 1991, Lauda Air Flight 004
, operated by a Boeing 767
, crashed after the left engine thrust reverser deployed in-flight for reasons that could not be determined. The crash
of a TAM Airlines Fokker 100 in 1996 was attributed to the deployment of the thrust reverser on No. 2 engine. The aircraft rolled to the right and crashed in a populated area of São Paulo
, Brazil
. In 2009, a Boeing 707
operated by Azza Transport
crashed
shortly after taking off; upon examining the wreckage of the aircraft, investigators found the No. 4 engine thrust reverser had deployed.
United Airlines
United Air Lines, Inc., is the world's largest airline with 86,852 employees United Air Lines, Inc., is the world's largest airline with 86,852 employees United Air Lines, Inc., is the world's largest airline with 86,852 employees (which includes the entire holding company United Continental...
Douglas DC-6
Douglas DC-6
The Douglas DC-6 is a piston-powered airliner and transport aircraft built by the Douglas Aircraft Company from 1946 to 1958. Originally intended as a military transport near the end of World War II, it was reworked after the war to compete with the Lockheed Constellation in the long-range...
named Mainliner Idaho crashed shortly after taking off from Long Island MacArthur Airport
Long Island MacArthur Airport
Long Island MacArthur Airport, formerly known as Islip Airport is a public airport located on Long Island, in Ronkonkoma, Town of Islip, Suffolk County, New York, United States. It is seven miles northeast of the central business district of Islip hamlet...
, in Ronkonkoma
Ronkonkoma, New York
Ronkonkoma is a census-designated place on Long Island in the Town of Islip, Suffolk County, New York, United States. The population was 20,029 at the 2000 census...
, Islip
Islip (town), New York
The Town of Islip is one of ten towns in Suffolk County, New York . Located on the south shore of Long Island, the town population was 322,612 at the 2000 census. The smaller, unincorporated hamlet of Islip lies within the town.-Demographics:...
, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The aircraft, registration number
Aircraft registration
An aircraft registration is a unique alphanumeric string that identifies a civil aircraft, in similar fashion to a licence plate on an automobile...
N37512, was performing an instrument rating
Instrument rating
Instrument rating refers to the qualifications that a pilot must have in order to fly under IFR . It requires additional training and instruction beyond what is required for a Private Pilot certificate or Commercial Pilot certificate, including rules and procedures specific to instrument flying,...
check flight, when, shortly after taking off, it began banking to the right. Seconds after climbing through 150 feet (45.7 m), the aircraft turned through 90 degrees, causing the nose to drop suddenly, before it impacted with the ground.
A subsequent investigation found that the flight crew were simulating an engine failure, which involved a member of the crew pulling back the throttle
Throttle
A throttle is the mechanism by which the flow of a fluid is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases , but usually decreased. The term throttle has come to refer, informally and incorrectly, to any mechanism by which...
lever for engine No.
Aircraft engine position number
Aircraft engine position number is a method to identify the location of engines on multi-engined aircraft. Aircraft engines are numbered from left to right from the view of the pilot looking forward.-Twin-engined aircraft:* #1 - port - on the left...
4 prior to taking off. Investigators found that if the throttle lever was pulled back too far, however, it would cause the propeller to reverse
Controllable pitch propeller
A controllable pitch propeller or variable pitch propeller is a type of propeller with blades that can be rotated around their long axis to change their pitch...
—a feature designed to slow the aircraft
Thrust reversal
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration...
upon landing. Once the landing gear was raised, the crew would have to raise a metal flag in the cockpit to bring the propeller blades back into the correct position, since a safety device prevented electric power from operating the rotating mechanism at the roots of the blades unless the aircraft was on the ground or the flag was manually raised. Investigators from the Civil Aeronautics Board (CAB) concluded that one of the flight crew applied full power to No. 4 engine, thinking this would bring the aircraft out of the increasing bank. But because the blades were reversed and the flag was not raised, the dramatically increased reverse thrust caused the DC-6 to spiral out of control. The investigators also concluded that the suddenness of the bank and dive meant the flight crew had little chance to recover the aircraft before impact.
In the aftermath of the accident, the Civil Aeronautics Administration (CAA) issued an Airworthiness Directive
Airworthiness Directive
An Airworthiness Directive is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics or other system exists and must be corrected....
ordering all DC-6 and DC-6B aircraft be fitted with a manual device which could prevent the inadvertent reversal of the propeller blades. United Airlines also stated they had begun installing reverse thrust indicator lights in the cockpits of their DC-6 aircraft, which would warn pilots when a propeller had reversed.
History
On April 4, 1955, a United Airlines check captain, Stanley C. Hoyt, age 45, was carrying out instrument ratingInstrument rating
Instrument rating refers to the qualifications that a pilot must have in order to fly under IFR . It requires additional training and instruction beyond what is required for a Private Pilot certificate or Commercial Pilot certificate, including rules and procedures specific to instrument flying,...
checks on two of the airline's pilots. Hoyt had been employed by United Airlines in 1937, and had 9,763 flying hours experience, 549 of which were in a DC-6. He was training the two pilots, Henry M. Dozier, age 40, and Vernis H. Webb, age 35, so they would be able to retain an instrument rating qualification, allowing them to fly under instrument flight rules
Instrument flight rules
Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
. The aircraft was a Douglas DC-6
Douglas DC-6
The Douglas DC-6 is a piston-powered airliner and transport aircraft built by the Douglas Aircraft Company from 1946 to 1958. Originally intended as a military transport near the end of World War II, it was reworked after the war to compete with the Lockheed Constellation in the long-range...
, registration
Aircraft registration
An aircraft registration is a unique alphanumeric string that identifies a civil aircraft, in similar fashion to a licence plate on an automobile...
N37512, serial number
Serial number
A serial number is a unique number assigned for identification which varies from its successor or predecessor by a fixed discrete integer value...
43001. The airframe had flown 22,068 flying hours, and had undergone an inspection 105 hours before the accident. The aircraft was powered by four Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...
R2800-CB16
Pratt & Whitney R-2800
The Pratt & Whitney R-2800 Double Wasp is a two-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of 2,804 in³ , and is part of the long-lived Wasp family....
engines, fitted with Hamilton Standard
Hamilton Standard
Hamilton Standard, an aircraft propeller parts supplier, was formed in 1929 when United Aircraft and Transport Corporation consolidated Hamilton Aero Manufacturing and Standard Steel Propeller into the Hamilton Standard Propeller Corporation. Other members of the corporation included Boeing,...
43E60-317 propellers.
The weather on the day of the accident was clear, although there was a strong wind of about 20 knots hitting the airfield from the southwest, with occasional gusts of wind as fast as 30 knots. The aircraft made several circuits, taking off and landing again, before eyewitnesses observed the aircraft standing at the end of the runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
and then taking off at about 15:50 Eastern Standard Time
Eastern Standard Time
Eastern Standard Time may refer to:*North American Eastern Time Zone, UTC-5*Australian Eastern Standard Time, UTC+10*An album by Hip Hop group Kooley High...
. Loaded with around 61000 pounds (27,669.1 kg), the aircraft was far below its maximum permissible weight and the center of gravity
Center of gravity
In physics, a center of gravity of a material body is a point that may be used for a summary description of gravitational interactions. In a uniform gravitational field, the center of mass serves as the center of gravity...
was within the prescribed limits for the model of aircraft.
Between 1500 feet (457.2 m) and 1800 feet (548.6 m) down the runway, the aircraft reached take-off speed
V speeds
In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft including fixed-wing aircraft, gliders, autogiros, helicopters, and dirigibles...
, lifted off the ground, and began climbing normally as the crew retracted the landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...
. Upon climbing through 50 feet (15.2 m), however, the aircraft began banking
Banked turn
A banked turn is a turn or change of direction in which the vehicle banks or inclines, usually towards the inside of the turn. The bank angle is the angle at which the vehicle is inclined about its longitudinal axis with respect to its path....
right. The climbing bank continued to increase at a rate which alarmed witnesses, and soon after the aircraft rotated through 90°
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
(at which point the wings were vertical to the ground). At a height of around 150 feet (45.7 m), with all four engines producing take-off thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
, the nose began to fall, and the aircraft stalled
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
. The right wing and nose impacted with the ground, causing the fuselage to cartwheel over, before the aircraft came to rest the correct side up and was engulfed in flames. Though emergency services at Long Island MacArthur responded to the crash, all three members of the flight crew had been killed on impact. The aircraft was destroyed by the post-crash fire.
Wreckage examination
The Civil Aeronautics Board (CAB), the organization charged with investigating the accident, went to Long Island MacArthur Airport to examine the wreckage. Upon hearing reports from witnesses of the crash that the aircraft appeared to have rotated and begun climbing normally before it began banking sharply to the right, investigators examined the four charred engines. While they had all been severely damaged by the impact and subsequent fire, it was concluded that all four were producing power at the point of impact. The CAB could not conclusively determine the amount of power being produced, but investigators stated there was no evidence found in the wreckage that suggested the engines might have suffered an operational failure.Investigators were also able to determine all of the flight control surfaces, including the elevators
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...
, aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s and rudder
Rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
, were functioning correctly at the point of the crash, and it was also found there were no faults in the flight control system of the aircraft. The flaps
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
, it was found, were extended to between 15° and 20°, the standard setting for take-off. Investigators did discover, however, that the propeller blades of No. 4 engine—the engine on the far right side of the aircraft—were reversed. While the blades of Nos. 1, 2 and 3 engines were at 34° positive pitch
Blade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...
(also standard for take-off), the blades of No. 4 engine were set at full reverse pitch—minus 8°.
Reversed thrust
The propellers of a DC-6 are designed to provide reverse thrustThrust reversal
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration...
when the aircraft touches down. When this feature is activated, the propellers begin producing thrust in the opposite direction, propelling the aircraft backwards to slow it down. When the crew then retards the throttle levers, electric mechanisms in the propeller hub rotate the blades
Controllable pitch propeller
A controllable pitch propeller or variable pitch propeller is a type of propeller with blades that can be rotated around their long axis to change their pitch...
to a position in which they will provide reverse thrust. Should a crew need to perform a go-around
Go-around
A go-around is an aborted landing of an aircraft that is on final approach.- Origin of the term :The term arises from the traditional use of traffic patterns at airfields. A landing aircraft will first join the circuit pattern and prepare for landing in an orderly fashion...
, they could restore the thrust levers to a positive position and again produce forward thrust, allowing them to execute the maneuver.
The Douglas Aircraft Company
Douglas Aircraft Company
The Douglas Aircraft Company was an American aerospace manufacturer, based in Long Beach, California. It was founded in 1921 by Donald Wills Douglas, Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas...
, however, designed a system that would prevent the accidental reversal of propeller blades in-flight. During development of the DC-6, the company installed a system that cut electrical power to the mechanisms which rotated the blades while the airplane was in the air. When there was enough weight on the landing gear
Landing Gear
Landing Gear is Devin the Dude's fifth studio album. It was released on October 7, 2008. It was his first studio album since signing with the label Razor & Tie. It features a high-profile guest appearance from Snoop Dogg. As of October 30, 2008, the album has sold 18,906 copies.-Track...
(which would only be the case when the aircraft was on the ground), a switch which supplied electrical power to the mechanisms was closed—meaning that when the aircraft touched down the blades could be reversed and thus the airplane could be slowed. When the switch was closed, a red flag would swing into view in the cockpit of the aircraft, warning the crew that the blades could be reversed. Should the switch fail to close upon landing, the flag could be raised manually and electrical power to the mechanisms would be restored. When the aircraft took off, electrical power would be cut to the mechanisms so that the propeller blades could not be inadvertently reversed, and the red flag swung out of sight. Reverse thrust warning lamps, which would have warned the crew if the propellers were reversed, were not fitted on Mainliner Idaho.
Flight tests
The CAB carried out flight tests using a DC-6. They found that if the propellers were reversed prior to take-off they would not, if the flag was not raised, be rotated automatically again in the air to produce forward thrust if full power was applied. Tests performed by United Airlines showed that, if the propellers of just one engine were reversed and full power was applied to all four engines, then the aircraft would spiral into a dive. If METO (maximum except take-off) power was applied to Nos. 1, 2 and 3 engines, and full reverse thrust was applied to engine No. 4, then the aircraft would become uncontrollable.If full left aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
was applied, the aircraft could be recovered for a short period of time, but a violent turn to the right would continue, and the competing forces would cause the aircraft to stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
, and violently roll and pitch down. Flight tests, investigators said, accurately reproduced what happened to Mainliner Idaho during the accident sequence. The tests performed by United and by the investigators showed that if, after the aircraft became airborne, full power was applied to an engine whose propellers were reversed, the propellers would produce not positive thrust, but increased reverse thrust. One aviation author wrote of the crash,
Conclusions
While the wreckage was being examined, investigators found that all four engines were producing thrust at the time of impact. There were only two ways that the propeller could be reversed during the take-off sequence. Investigators ruled out electrical malfunction since, after detailed examination of the engine hub, there was no evidence found of this happening. Therefore, it was concluded that the only way the propeller could have been reversed was through an unintentional crew action. Although there was no formal evidence that a simulated engine failure was being performed, statements submitted by witnesses suggested that it was likely this was the case. United Airlines procedure calls for No. 4 engine to be shut down in a simulated engine failure—the same engine which was found at the crash site with its propellers reversed.The investigation concluded that the accident sequence began when the check pilot, while the aircraft was on the ground, retarded the throttle lever for No. 4 engine past the idle position, and therefore reversed the propellers of the aircraft. Once the airplane took off and started banking to the right, it would have been a natural reaction for one of the flight crew to increase power to No. 4 engine, thinking that by doing so the engine would start producing positive thrust and the aircraft could be recovered. However, since the metal flag was not raised, there was no electrical power to the rotating mechanisms—and increasing power to No. 4 engine would only have created more reverse thrust.
The final accident report concluded that there was no time for the crew to react, since the dive began so suddenly, and there was no way for the crew to recover the aircraft. "Control will be lost so quickly that there is little, if anything, that the pilot can do if it occurs at low altitude," the report stated. "He must recognize what is occurring, analyze it, and take action to unreverse in a very limited amount of time. It is doubtful that unreversing could have been accomplished in this instance before control was lost." On October 4, 1955, the CAB released the final accident report, which concluded the reversal of the propellers and subsequent increase in power to No. 4 engine had caused the accident.
Technological advances
Following the accident, the Civil Aeronautics Administration (CAA) issued an Airworthiness DirectiveAirworthiness Directive
An Airworthiness Directive is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics or other system exists and must be corrected....
ordering all DC-6 and DC-6B aircraft to be fitted with a sequence gate latch, known as a Martin bar. The device is a metal bar which a crew would manually swing in front of the thrust levers over the idle line, physically preventing the thrust levers from being retarded into the reverse position. According to the CAB report, a United Airlines engineer told investigators the Martin bar should make propeller reversal "a more reliable and safer device [than the system fitted to Mainliner Idaho] ... with its numerous switches, relays, and automatic operation."
United Airlines issued a statement saying it had begun installing the device on its fleet of DC-6 and DC-6B aircraft one week before the accident, having used it successfully in service on their fleet of Douglas DC-7
Douglas DC-7
The Douglas DC-7 is an American transport aircraft built by the Douglas Aircraft Company from 1953 to 1958. It was the last major piston engine powered transport made by Douglas, coming just a few years before the advent of jet aircraft such as the Boeing 707 and Douglas DC-8.-Design and...
aircraft. A Martin bar had not yet been fitted on Mainliner Idaho. United Airlines also said a program had begun to install reverse thrust indicator lights on all their DC-6 and DC-6B aircraft. The signals, fitted in the cockpit of the aircraft, would have warned the flight crew that the thrust lever had been pulled back too far, and the propellers had been reversed.
Similar accidents
Since the crash, there have been several other accidents involving reverse thrust. A Douglas DC-8Douglas DC-8
The Douglas DC-8 is a four-engined narrow-body passenger commercial jet airliner, manufactured from 1958 to 1972 by the Douglas Aircraft Company...
operating United Airlines Flight 859
United Airlines Flight 859
United Airlines Flight 859 was a scheduled passenger flight that crashed on July 11, 1961 during landing at Stapleton International Airport, Denver, Colorado...
crashed in 1961 when the first officer attempted to reverse all four engines during the landing roll. The left engines remained in forward thrust, while the right engines went into reverse, causing the aircraft to veer rapidly to the right and collide with airport construction vehicles, killing 18 of the 122 people aboard.
Japan Airlines Flight 350
Japan Airlines Flight 350
Japan Airlines Flight 350 was a McDonnell Douglas DC-8-61, aircraft registration , on a domestic scheduled passenger flight from Fukuoka, Japan, to Tokyo. The airplane crashed 9 February 1982 on approach to Tokyo Haneda Airport in Tokyo Bay...
, a DC-8, crashed in 1982 short of the runway in Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
, after the mentally ill captain attempted suicide during the final approach phase of the flight, by putting the inboard engines into reverse thrust. Of the 174 people aboard, 24 died.
In 1991, Lauda Air Flight 004
Lauda Air Flight 004
Lauda Air Flight 004 was an international passenger flight that crashed due to a thrust reverser deployment of the number 1 engine in flight.-History of the flight:...
, operated by a Boeing 767
Boeing 767
The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...
, crashed after the left engine thrust reverser deployed in-flight for reasons that could not be determined. The crash
TAM Transportes Aéreos Regionais Flight 402
TAM Transportes Aéreos Regionais Flight 402 was a Fokker 100 airliner, operating as a scheduled domestic flight from Congonhas/São Paulo International Airport in São Paulo, Brazil to Santos Dumont Airport in Rio de Janeiro on October 31, 1996, which crashed shortly after take-off, killing a total...
of a TAM Airlines Fokker 100 in 1996 was attributed to the deployment of the thrust reverser on No. 2 engine. The aircraft rolled to the right and crashed in a populated area of São Paulo
São Paulo
São Paulo is the largest city in Brazil, the largest city in the southern hemisphere and South America, and the world's seventh largest city by population. The metropolis is anchor to the São Paulo metropolitan area, ranked as the second-most populous metropolitan area in the Americas and among...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
. In 2009, a Boeing 707
Boeing 707
The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...
operated by Azza Transport
Azza Transport
Azza Transport is a cargo airline based in Khartoum, Sudan. It operates a cargo charter service throughout Africa and the Middle East and is planning services for Europe. Its main base is Khartoum International Airport.-History:...
crashed
Azza Transport Flight 2241
Azza Transport Flight 2241 was a scheduled cargo flight from Sharjah, United Arab Emirates, to Khartoum, Sudan, which crashed on 21 October 2009.-Aircraft:...
shortly after taking off; upon examining the wreckage of the aircraft, investigators found the No. 4 engine thrust reverser had deployed.
See also
- Air safetyAir safetyAir safety is a term encompassing the theory, investigation and categorization of flight failures, and the prevention of such failures through regulation, education and training. It can also be applied in the context of campaigns that inform the public as to the safety of air travel.-United...
- List of accidents and incidents involving commercial aircraft
- 1955 in aviation1955 in aviationThis is a list of aviation-related events from 1955:- Events :* The United Kingdoms first atomic bomber unit, the Royal Air Forces No. 138 Squadron, becomes operational, flying Vickers Valiants.-January:...