National Airlines Flight 27
Encyclopedia
On November 3, 1973, a National Airlines (NA)
DC-10-10
aircraft (N60NA) was operating as a scheduled passenger flight between Miami and San Francisco with intermediate stops at New Orleans, Houston, and Las Vegas
(NA Flight 27).
At about 4:40 p.m., while the aircraft was cruising at 39000 feet (11,887.2 m) 65 miles southwest of Albuquerque, the No. 3 engine fan assembly disintegrated (uncontained failure
) and its fragments penetrated the fuselage, the Nos. 1 and 2 engine nacelles (which contain those engines), and the right wing area. The resultant damage caused decompression of the aircraft cabin and the loss of certain electrical and hydraulic systems.
The flight crew initiated an emergency descent, and the aircraft was landed safely at Albuquerque International Airport 19 minutes after the engine failed. The 115 passengers and 12 crewmembers exited the aircraft by using the evacuation slides. As a result of the accident, one passenger died and 24 persons were treated for smoke inhalation
, ear problems, and minor abrasions. The plane was repaired and was later flown by Pan Am (as Clipper Meteor)
One passenger, G.F. Gardner of Beaumont, Texas
, was partially sucked into an opening left when a cabin window failed, after it too was struck by engine fragments. He was temporarily retained in that position by his seatbelt. "Efforts to pull the passenger back into the airplane by another passenger were unsuccessful, and the occupant of seat 17H was forced entirely through the cabin window." The New Mexico State Police
and local organizations searched extensively for the missing passenger. A computer analysis was made of the possible falling trajectories, which narrowed the search pattern. However, the search effort was unsuccessful, and the body of the passenger was not recovered until two years later, when a crew constructing tracks for the Very Large Array
radio telescope came upon his skeletal remains.
determined the probable cause of this accident was the disintegration of the No. 3 engine fan assembly
as a result of an interaction between the fan blade tips and the fan case. The fan-tip rub condition was caused by the acceleration of the engine to an abnormally high fan speed which initiated a multiwave, vibratory resonance
within the fan section of the engine. The precise reason or reasons for the acceleration and the onset of the destructive vibration could not be determined conclusively.
However, it is clear that the captain
and flight engineer
's irresponsible actions were to blame. They were experimenting with the autothrottle
system, which supplied the instruments that measure the rotational speed of each engine's low pressure compressor. The cockpit voice recording
contains the following conversation just prior to the number 3 engine exploding:
Captain William Brookes, who had been a National Airlines pilot since 1946 and who should have known better responds, "Yeah, let's see here."
[At the instant he says the word "nose" there is the sound of the number 3 engine exploding followed by ratcheting sounds.]
By playing with the autothrottle controls - in what amounted to an in-flight failure analysis
test of the autothrottle system - the crew managed to produce a condition where the engines were pushed to higher rotation speeds than they were designed for. According to audio analysis of the CVR tape, all three engines surged (#1 to 105% of nominal maximum power, #2 to 107% and number 3, which failed, to 110%).
What the flight deck crew was trying to do was to determine the relationship between the fan speed indicator (N1) and the automatic flight control systems. The flight engineer
disconnected the electrical circuit breakers for all three low speed fan tachometer
s while the pilot
reduced the airspeed
by 5 knots (9.8 km/h). Once the throttle
s automatically restarted, the pilot disconnected the autothrottle
. The crew then heard the explosion
.
The CF6-6D engines used on the aircraft were designed to never exceed the maximum N1 speed limit speed of 111% (of nominal maximum speed). The #3 engine was at 99% N1 at the time that the initial explosion sound was first heard. It continued to accelerate too, while the other two engines reached a maximum speed of 107% N1. "The speed of engine #3 was no longer discernible after achieving 110% N1 during acceleration, hence the maximum speed attained could not be determined."
According to the NTSB, "The precise reason or reasons for the acceleration and the onset of the destructive vibration could not be determined conclusively," but enough was learned to prevent the occurrence of similar events. The speed of the engine at the time of the accident caused a resonance wave
to occur in the fan assembly when the fan blades began to make contact with the fan shroud. The existing engines had a rearward blade retaining capability of 18,000 pounds to prevent the blades from "walking" towards the front of the aircraft and part with the fan disk
. That was not enough. As a result of this accident, GE re-designed the engine so that the blade retaining capability was increased to 60,000 pounds, and that change was incorporated into all engines already in service.
National Airlines (NA)
National Airlines was an airline founded in 1934 and was headquartered on the grounds of Miami International Airport in unincorporated Miami-Dade County, Florida, United States near Miami.- History :...
DC-10-10
McDonnell Douglas DC-10
The McDonnell Douglas DC-10 is a three-engine widebody jet airliner manufactured by McDonnell Douglas. The DC-10 has range for medium- to long-haul flights, capable of carrying a maximum 380 passengers. Its most distinguishing feature is the two turbofan engines mounted on underwing pylons and a...
aircraft (N60NA) was operating as a scheduled passenger flight between Miami and San Francisco with intermediate stops at New Orleans, Houston, and Las Vegas
Las Vegas, Nevada
Las Vegas is the most populous city in the U.S. state of Nevada and is also the county seat of Clark County, Nevada. Las Vegas is an internationally renowned major resort city for gambling, shopping, and fine dining. The city bills itself as The Entertainment Capital of the World, and is famous...
(NA Flight 27).
At about 4:40 p.m., while the aircraft was cruising at 39000 feet (11,887.2 m) 65 miles southwest of Albuquerque, the No. 3 engine fan assembly disintegrated (uncontained failure
Turbine engine failure
A turbine engine failure refers to an incident wherein a turbine engine in an aircraft unexpectedly stops producing power because of a part malfunction, in the absence of circumstances such as fuel exhaustion.-Nature of failures:...
) and its fragments penetrated the fuselage, the Nos. 1 and 2 engine nacelles (which contain those engines), and the right wing area. The resultant damage caused decompression of the aircraft cabin and the loss of certain electrical and hydraulic systems.
The flight crew initiated an emergency descent, and the aircraft was landed safely at Albuquerque International Airport 19 minutes after the engine failed. The 115 passengers and 12 crewmembers exited the aircraft by using the evacuation slides. As a result of the accident, one passenger died and 24 persons were treated for smoke inhalation
Smoke inhalation
Smoke inhalation is the primary cause of death in victims of indoor fires.Smoke inhalation injury refers to injury due to inhalation or exposure to hot gaseous products of combustion. This can cause serious respiratory complications....
, ear problems, and minor abrasions. The plane was repaired and was later flown by Pan Am (as Clipper Meteor)
One passenger, G.F. Gardner of Beaumont, Texas
Beaumont, Texas
Beaumont is a city in and county seat of Jefferson County, Texas, United States, within the Beaumont–Port Arthur Metropolitan Statistical Area. The city's population was 118,296 at the 2010 census. With Port Arthur and Orange, it forms the Golden Triangle, a major industrial area on the...
, was partially sucked into an opening left when a cabin window failed, after it too was struck by engine fragments. He was temporarily retained in that position by his seatbelt. "Efforts to pull the passenger back into the airplane by another passenger were unsuccessful, and the occupant of seat 17H was forced entirely through the cabin window." The New Mexico State Police
New Mexico State Police
The New Mexico State Police is the state police agency for New Mexico, which has jurisdiction anywhere in the state. It was created to protect the lives, property and constitutional rights of people in New Mexico...
and local organizations searched extensively for the missing passenger. A computer analysis was made of the possible falling trajectories, which narrowed the search pattern. However, the search effort was unsuccessful, and the body of the passenger was not recovered until two years later, when a crew constructing tracks for the Very Large Array
Very Large Array
The Very Large Array is a radio astronomy observatory located on the Plains of San Agustin, between the towns of Magdalena and Datil, some fifty miles west of Socorro, New Mexico, USA...
radio telescope came upon his skeletal remains.
Investigation
The National Transportation Safety BoardNational Transportation Safety Board
The National Transportation Safety Board is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine...
determined the probable cause of this accident was the disintegration of the No. 3 engine fan assembly
Fan disk
A fan disk is the part of a turbofan jet engine that contains the fan blades. It is considered one of the most critical components of the engine and has four main functions:...
as a result of an interaction between the fan blade tips and the fan case. The fan-tip rub condition was caused by the acceleration of the engine to an abnormally high fan speed which initiated a multiwave, vibratory resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
within the fan section of the engine. The precise reason or reasons for the acceleration and the onset of the destructive vibration could not be determined conclusively.
However, it is clear that the captain
Pilot in command
The pilot in command of an aircraft is the person aboard the aircraft who is ultimately responsible for its operation and safety during flight. This would be the "captain" in a typical two- or three-pilot flight crew, or "pilot" if there is only one certified and qualified pilot at the controls of...
and flight engineer
Flight engineer
Flight engineers work in three types of aircraft: fixed-wing , rotary wing , and space flight .As airplanes became even larger requiring more engines and complex systems to operate, the workload on the two pilots became excessive during certain critical parts of the flight regime, notably takeoffs...
's irresponsible actions were to blame. They were experimenting with the autothrottle
Autothrottle
An autothrottle allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling fuel flow...
system, which supplied the instruments that measure the rotational speed of each engine's low pressure compressor. The cockpit voice recording
CVR
CVR is an abbreviation that may refer to:* Det Centrale Virksomhedsregister, a Danish register of businesses* Cimarron Valley Railroad* Cockpit voice recorder, a type of aircraft flight recorder which records audio information....
contains the following conversation just prior to the number 3 engine exploding:
- Flight Engineer: "Wonder, wonder if you pull the N1 tachTachometerA tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
will that, -- autothrottle respond to N1?" - Captain: "Gee, I don't know."
- Flight Engineer: "You want to try it and see?"
Captain William Brookes, who had been a National Airlines pilot since 1946 and who should have known better responds, "Yeah, let's see here."
- Flight Engineer: "You're on speed right now though."
- Captain: "Yeah."
- Flight Engineer: "You know what I mean if your annunciated speed - if you got, ---"
- Captain: "Still got 'em."
- Flight Engineer: "Well -- haven't got it --"
- Captain: "There it is."
- Flight Engineer: "I guess it does."
- Captain: "Yeah, I guess it does -- right on the nose."
[At the instant he says the word "nose" there is the sound of the number 3 engine exploding followed by ratcheting sounds.]
- Captain: "[expletive deleted] what was that?"
By playing with the autothrottle controls - in what amounted to an in-flight failure analysis
Failure analysis
Failure analysis is the process of collecting and analyzing data to determine the cause of a failure. It is an important discipline in many branches of manufacturing industry, such as the electronics industry, where it is a vital tool used in the development of new products and for the improvement...
test of the autothrottle system - the crew managed to produce a condition where the engines were pushed to higher rotation speeds than they were designed for. According to audio analysis of the CVR tape, all three engines surged (#1 to 105% of nominal maximum power, #2 to 107% and number 3, which failed, to 110%).
What the flight deck crew was trying to do was to determine the relationship between the fan speed indicator (N1) and the automatic flight control systems. The flight engineer
Flight engineer
Flight engineers work in three types of aircraft: fixed-wing , rotary wing , and space flight .As airplanes became even larger requiring more engines and complex systems to operate, the workload on the two pilots became excessive during certain critical parts of the flight regime, notably takeoffs...
disconnected the electrical circuit breakers for all three low speed fan tachometer
Tachometer
A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
s while the pilot
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
reduced the airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
by 5 knots (9.8 km/h). Once 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...
s automatically restarted, the pilot disconnected the autothrottle
Autothrottle
An autothrottle allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling fuel flow...
. The crew then heard the explosion
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...
.
The CF6-6D engines used on the aircraft were designed to never exceed the maximum N1 speed limit speed of 111% (of nominal maximum speed). The #3 engine was at 99% N1 at the time that the initial explosion sound was first heard. It continued to accelerate too, while the other two engines reached a maximum speed of 107% N1. "The speed of engine #3 was no longer discernible after achieving 110% N1 during acceleration, hence the maximum speed attained could not be determined."
According to the NTSB, "The precise reason or reasons for the acceleration and the onset of the destructive vibration could not be determined conclusively," but enough was learned to prevent the occurrence of similar events. The speed of the engine at the time of the accident caused a resonance wave
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
to occur in the fan assembly when the fan blades began to make contact with the fan shroud. The existing engines had a rearward blade retaining capability of 18,000 pounds to prevent the blades from "walking" towards the front of the aircraft and part with the fan disk
Fan disk
A fan disk is the part of a turbofan jet engine that contains the fan blades. It is considered one of the most critical components of the engine and has four main functions:...
. That was not enough. As a result of this accident, GE re-designed the engine so that the blade retaining capability was increased to 60,000 pounds, and that change was incorporated into all engines already in service.