Description

On 27 January 2009, an ATR 42-300 being operated by Empire Airlines on a scheduled cargo flight from Fort Worth Alliance to Lubbock was making a night Instrument Landing System (ILS) approach in Instrument Meteorological Conditions (IMC) to runway 17R at destination when it stalled and crashed short of the runway. The aircraft caught fire and was in any case effectively already destroyed by the impact. Both crew members were injured, one seriously.

Investigation

An Investigation was carried out by the National Transportation Safety Board (USA) (NTSB). It was established that the aircraft was correctly loaded. Icing conditions prevailed but no evidence that they were outside the certification of the aircraft or otherwise contributed to the outcome was found.

The aircraft commander was experienced but the First Officer, designated as PF had low aircraft type experience and lacked much previous experience of flight in icing conditions. En route, it had been anticipated that the destination weather conditions would preclude the First Officer remaining as PF and so the approach brief had been given by the aircraft commander. In the event, conditions were better than expected with overcast at 500 feet, a light northerly breeze and visibility 3200 metres and so the First Officer had remained as PF.

After descent through an inversion layer, when airframe ice previously accumulated had been shed, icing conditions with freezing drizzle were re-entered below 6000 feet. The ILS LLZ for runway 17R was captured with the AP engaged, but the PF failed to reduce power appropriately on intercepting the GS so that airspeed became excessive. The response was a rapid reduction in power almost to Flight Idle. At about 1400 feet aal, Flap 15 and Gear Down were called but the selected flap 15 failed to deploy properly with only partial deployment on one wing and nil deployment on the other. The aircraft commander as PM failed to action the corresponding Quick Reference Handbook (QRH) drill and became so pre-occupied with the flap problem that he ceased monitoring the actions of the PF. The problem also distracted the PF from managing the aircraft and airspeed reduced to the point where a brief stick shaker activation occurred at 900 feet aal and the AP disconnected. The First Officer, having tentatively asked if she should fly a go around and been firmly instructed to continue descent , applied power and began to fly the aircraft manually. However, in evident difficulty, she willingly accepted the aircraft commander’s offer to take control at 700ft aal with the aircraft at the applicable minimum safe speed for zero flap in icing conditions of 143 KIAS. Then, just after the aircraft emerged from the cloud base at 500 feet aal, there was a second stick shaker activation and a GPWS/TAWS ‘PULL UP’ Warning. Thereafter, there was no effective response to the stick shaker - speed was 124 KIAS by 200 feet aal and the aircraft stalled, crashed and caught fire.

It was established that when the flight crew had selected 15° flap, flap asymmetry had occurred with the left flaps extending 8° to 10° and the right flaps not extending at all. Flight Data Recorder (FDR) data also showed that the flaps returned to symmetry deployed at about 4.5° about 25 seconds before ground impact. Impact and post accident fire damage made it impossible for the Investigation to determine the reason for the flap asymmetry, but it was considered that the absence of a flap asymmetry caution was an unsatisfactory aspect of the situation faced by the crew.

It was considered that the presence of airframe ice accretion which was within the capabilities of the aircraft systems did not negate the importance of adhering to SOPs and initiating a go around in response to what had clearly become an unstabilised approach characterized by excessive deviation from the ILS GS, a rate of descent of > 1000 fpm and airspeed less than the required approach speed. However, there were differences of opinion amongst the NTSB Board Members involved in approving the In Investigation Report especially in respect of the validity of flight in SLD conditions based on the certification of the aircraft type for flight in icing conditions.

The Captain’s response to the flap fault was considered by the Investigation to be contrary to his training given that his recognition that the aircraft had “no flaps” could reasonably be taken to indicate that he had sufficient information to recognise that the initiation of a go-around and the actioning of the appropriate QRH drill were required. Although some of the airspeed bugs (including the ASI internal bugs) were not set to the appropriate approach airspeeds and were not reset following recognition of the flap anomaly, it was concluded that the pilots had had an adequate reference for the minimum safe airspeed because the airspeed for a no-flap approach in icing conditions was correctly briefed as 143 knots, and the ‘red’ airspeed bugs were set near that value.

The formally stated Findings of the Investigation included the following:

• The airplane was controllable with the flap asymmetry and airframe ice contamination and could have been manoeuvred and landed safely if the appropriate airspeed had been maintained.
• The Captain’s failure to immediately respond to the aural stall warning, the stick shaker and the TAWS activation resulted in his inability to arrest the airplane’s descent and avoid impact with the ground.
• Had the Captain complied with standard operating procedures in response to the flap anomaly, unstabilised approach, stick shaker and (the) terrain awareness and warning system warning and initiated a go-around manoeuvre, the accident likely would not have occurred.
• The First Officer’s failure to maintain airspeed while acting as the pilot flying likely resulted from being distracted by the flap anomaly, the Captain’s actions in response to it, and the control force inputs needed to maintain aircraft control.
• The Captain’s failure to call out the First Officer’s airspeed deviations resulted directly from his preoccupation with performing an inappropriate, nonstandard procedure in response to the flap anomaly.
• The First Officer’s failure to assert herself to the Captain and initiate a go-around manoeuvre when she recognised the unstabilised approach likely resulted from the steep authority gradient in the cockpit and the First Officer’s minimal training on assertiveness; further, the Captain’s quick dismissal of the First Officer’s go-around inquiry likely discouraged the First Officer from voicing her continued concerns and challenging the Captain’s decision to continue the unstabilised approach.

The NTSB determined that Probable Cause of the accident was:

the flight crew’s failure to monitor and maintain a minimum safe airspeed while executing an instrument approach in icing conditions, which resulted in an aerodynamic stall at low altitude. It was also determined that contributing to the accident were:

1. the flight crew’s failure to follow published standard operating procedures in response to a flap anomaly,
2. the Captain’s decision to continue with the unstabilised approach,
3. the flight crew’s poor crew resource management, and
4. fatigue due to the time of day in which the accident occurred and a cumulative sleep debt, which likely impaired the Captain’s performance.

Nine Safety Recommendations were made as a result of this investigation, all to the Federal Aviation Administration (FAA):

• Require that role-playing or simulator-based exercises that teach First Officers to assertively voice their concerns and that teach Captains to develop a leadership style that supports first officer assertiveness be included as part of the already required crew resource management training for 14 Code of Federal Regulations Part 121, 135, and 91 subpart K pilots. (A-11-39)
• Prohibit all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators of pneumatic deice boot-equipped airplanes from dispatching or deliberately operating these airplanes in known freezing rain or freezing drizzle of any intensity, unless the airplane manufacturer has demonstrated that the airplane model can safely operate in those conditions. (A-11-40)
• Review the approved pilot, dispatcher, and flight follower training programs and procedures for all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators and require revisions to the programs and procedures, as necessary, to include standardized training and aircraft-specific information to educate pilots, dispatchers, and flight followers of the dangers of flight operations in freezing precipitation and of the differences between ground deicing considerations and in-flight icing operations. (A-11-41)
• Develop a method to quickly communicate information regarding the number of persons on board and the presence of hazardous materials to emergency responders when airport emergency response or search and rescue is activated. (A-11-42)
• Amend Advisory Circular 150/5200-30C to include guidance on monitoring and ensuring the operability of emergency response and mutual aid gates during winter operations. (A-11-43)
• Require all operators of Avions de Transport Régional Aerospatiale Alenia ATR 42- and ATR 72-series airplanes to retrofit the airplanes with an aircraft performance monitoring system if they are not already so equipped. (A-11-44)
• Require all Avions de Transport Régional Aerospatiale Alenia ATR 42-series airplanes to be equipped with a flap asymmetry annunciator light if they are not already so equipped. (A-11-45)
• Define and codify minimum simulator model fidelity requirements for aerodynamic degradations resulting from airframe ice accumulation. These requirements should be consistent with performance degradations that the National Transportation Safety Board and other agencies have extracted during the investigations of icing accidents and incidents. (A-11-46)
• Once the simulator model fidelity requirements requested in Safety Recommendation A-11-46 are implemented, require that flight crews of all aircraft certificated for flight in icing conditions be trained in flight training simulators that meet these fidelity requirements. Such simulation training should emphasize the following:
  1. cues for recognizing changes in the aircraft’s flight characteristics as airframe icing develops;
  2. procedures for monitoring and maintaining appropriate airspeeds in icing conditions, including the use of icing airspeed reference indices; and
  3. procedures for responding to decaying airspeed situations, stall protection system activation, and early stalls that can occur without stall protection system activation. (A-11-47)

The Final Report of the Investigation Accident Report NTSB/AAR-11/02 was adopted by the NTSB on 26 April 2011.

Further Reading

• Loss of Control
• Aerodynamic Stall Awareness and Avoidance
• Ice Formation on Aircraft
• Ice Contaminated Tailplane Stall
• Fatigue
• Adherence to SOPs (OGHFA BN)
• Crew Resource Management (OGHFA BN)