Photo: Pinnacle Airlines 3701 wreckage, from NTSB.

Eddie Sez:

This crew was nominated for a Darwin Award in 2004 and rightfully so. Their lack of professionalism deserves no less. But the incident also served to once again underline the fact many pilots do not understand the cause and remedy of an aerodynamic stall.

  • Aerodynamics — Not everyone who drives a car understands what is going on between the gas pedal and the tires but every pilot should know the difference between the relative wind and the chordline of a wing. See Basic Aerodynamics / Lift for more about this.

  • Stall Recovery — When a highly cambered wing is stalled there is only one way to get it out of the stall and years of simulator practice trying to hold every inch of altitude needs to be unlearned. See Basic Aerodynamics / Angle of Attack for more about AOA. See Abnormal Procedures / Stall Recovery for more about this.

Much has been made in this mishap about the possibility of both engines suffering a core lock, preventing a relight. A core lock occurs when an engine is shutdown at altitude and the cold temperature causes various parts of the engine to contract at different rates, preventing the compressor and turbine blades from spinning. It may or may not have been the case in this mishap but that misses the point. If there was a core lock, the pilots caused it by allowing their airspeed to get unacceptably low.

But there is one more factor that I think everyone has missed. When pilots who have never stalled a large airplane are trained exclusively in simulators, having an abnormal situation outside of the box can come as a shock. When in a panic, our brains often jump to an instinctual reaction (pull back on the yoke) and fail to think things through. The best way to deal with this is to desensitize oneself against the fear in a real airplane. More about this: Pilot Psychology / Panic.

This mishap does provide another lesson: if you are gliding an airplane to lower altitude in hopes of relighting the engines, keep an eye on the spool rotation. In a G450, for example, you cannot attempt a relight until 25,000 feet. It would be wise to keep both spools rotating at some speed during the descent.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.


Accident Report


Narrative

[NTSB AAR-07/01, ¶1.1.]


Analysis

[NTSB AAR-07/01, ¶1.27.1] Examination of the engines at the accident site found that neither engine exhibited classic rotational damage or ingestion evidence. The engines were disassembled and inspected at GE's manufacturing facility in Lynn, Massachusetts. The engine core rotors were rotated, and neither core was found seized. Teardown inspections found no mechanical failures or evidence of seizure in either engine. A materials investigation of the high pressure turbine seal hardware found no abnormal rotational marks.

[NTSB AAR-07/01, ¶1.18.2]

[NTSB AAR-07/01, ¶2.2.1]

[NTSB AAR-07/01, ¶2.2.2]

[NTSB AAR-07/01, ¶3.1]

[NTSB AAR-07/01, ¶2.2.3]

[NTSB AAR-07/01, ¶3.1]


Probable Cause

[NTSB AAR-07/01, ¶3.2] The National Transportation Safety Board determines that the probable causes of this accident were (1) the pilots' unprofessional behavior, deviation from standard operating procedures, and poor airmanship, which resulted in an in-flight emergency from which they were unable to recover, in part because of the pilots' inadequate training; (2) the pilots' failure to prepare for an emergency landing in a timely manner, including communicating with air traffic controllers immediately after the emergency about the loss of both engines and the availability of landing sites; and (3) the pilots' improper management of the double engine failure checklist, which allowed the engine cores to stop rotating and resulted in the core lock engine condition. Contributing to this accident were (1) the core lock engine condition, which prevented at least one engine from being restarted, and (2) the airplane flight manuals that did not communicate to pilots the importance of maintaining a minimum airspeed to keep the engine cores rotating.


See Also

Basic Aerodynamics / Low Speed Flight

Abnormal Procedures & Techniques / Aerodynamic Stall

Pilot Psychology / Complacency

Pilot Psychology / Panic


References

NTSB Aircraft Accident Report, AAR-0y/01, Crash of Pinnacle Airlines Flight 3701 Bombardier CL-600-2B19, N8396A, Jefferson City, Missouri October 14, 2004