On 29 October 2006, a Boeing 737-200 being operated by ADC Airlines on a scheduled domestic passenger flight from Abuja to Sokoto crashed shortly after taking off from runway 22 in normal daylight visibility into developing adverse weather conditions without communicating with ATC. The aircraft was subsequently located nearby and found to have been destroyed by impact and fire which led to the death of 96 of the 105 occupants, major injuries to 2 others and minor injuries to the other 7. There were no ground casualties.
An Investigation was begun by the Nigerian AIB. The Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) recordings were successfully downloaded. The very limited range of FDR parameters required the application of some complex methodology to derive the sequence of angle of attack and horizontal and vertical wind components experienced.
It was found that the aircraft had remained airborne for just 76 seconds after becoming airborne and to have crashed just under half a mile to the right the extended runway centreline about 400 metres beyond the upwind end of the runway. Site evidence indicated that the impact had occurred with the aircraft nose low and with extreme left bank. All the survivors were in the tail section of the aircraft which was detached at impact and remained substantially intact.
It was established that although the Captain had considerable flying experience, he had less than 400 hours command experience on type. The First Officer had considerable experience but there was no information on how much of this had been gained on the 737. Both pilots were Nigerian nationals but it was found that the First Officer had acquired his Nigerian licence by renewing one issued in Equatorial Guinea, the issue of which the Investigation was unable to find anything useful about. It was also noted that both pilots had received all their aircraft type training, both in the simulator and on the aircraft, from a single and authorised instructor/examiner. It was considered that this was entirely inappropriate because the practice “did not permit checks and balances and (facilitate) standardisation”. It was considered that “one instructor should have done the simulator training while another performed the final check (and) the same for the aircraft training and check”.
The Investigation found that the aircraft had been airworthy and correctly loaded. Based on CVR and FDR evidence, the flight sequence was reconstructed. During take off, the intensity of rain already falling had increased to heavy. When the First Officer made the “80 knots” call, the Captain responded with ‘ah’ instead of ‘checked’. Rotation was initiated five knots before the applicable Rotation Speed (Vr) of 138 knots and four seconds after the landing gear was selected up, the First Officer made the ‘V2’ call (which should have indicated that the speed was 143 knots) and two seconds later, the on board reactive wind shear warning was triggered as the aircraft encountered first positive and then negative horizontal wind shear. The recorded airspeed reached a maximum of 162 knots before rapidly reducing, in response to which the aircraft pitch attitude was reduced and then, as the negative shear took effect and height above ground rapidly reduced, a severe pitch up to between 30° and 35° was made. This gross exceedance of the stall angle of attack activated the stick shaker and both engines briefly experienced compressor stall because of the disrupted intake air flow. The aircraft became fully stalled and rolled to the left out of control with the Hard GPWS/TAWS Warning “Terrain, Terrain, Pull Up, Pull Up” activated and ground impact followed. Maximum height reached after take off as the initial positive shear was encountered was around 400 feet aal.
Track of aircraft from start of take off to impact position (Reproduced from the Official Report)
The Captain, as PF, had already remarked prior to beginning the take off roll that they should be ready for possible wind shear and ATC had passed some spot winds during the minutes prior to the beginning of the take of roll and noted at one point that the wind was ‘gusty’. The Investigation considered that “the prevailing gusty wind would have required the crew to delay their take off taking best practice and good airmanship into account.”
An aftercast of the weather conditions obtained by the Investigation showed that from only scattered Cumulus of insignificant development earlier in the morning, “explosive convective development” had then commenced and an isolated convective cell had formed and remained over Abuja with estimated tops at above 45,000 feet in just over an hour. In the half hour prior to the take off of the accident aircraft, this cell had continued to intensify with the estimated tops increasing to above 50,000 feet and satellite detection of cloud top temperature showing -77°C.
The Investigation found that although flight in adverse weather had been followed by loss of control, the crew response to the conditions was not in accordance with standard wind shear recovery procedure and noted that “the aircraft appeared to have (had) enough energy to fly through the adverse weather conditions” had these procedures been applied. However, it was considered that the simulator training the pilots had received had not adequately prepared them to handle the situation they found themselves (in). It was noted that the simulator used for the training did not have the same specification as their aircraft.
The ADC Airlines Operations Manual, which had been approved by the Nigerian CAA, was also found to have had no policy on aircraft operation in adverse and potentially hazardous atmospheric condition with the relevant section left blank. It was noted that had such a section been included, it “could have guided the pilots on the decision to go or not to go in adverse and potentially hazardous atmospheric conditions”.
The Investigation concluded that the Cause of the accident was “the pilot’s decision to take-off in known adverse weather conditions and failure to execute the proper wind shear recovery procedure resulted in operating the aircraft outside the safe flight regime, causing the aircraft to stall very close to the ground from which recovery was not possible."
The following Contributory Factors were also formally identified:
- Inability of the flight crew to apply windshear recovery procedures and the use of inappropriate equipment for windshear recovery procedure during simulator recurrency. Lack of Company Standard Operating Procedures (SOPs) for flight operations in adverse weather conditions.
- The coordination of responsibilities between the pilot-flying (PF) and pilot not flying (PNF) during their encounter with adverse weather situation was inconsistent with Standard Operating Procedures (SOPs) for the duties of the pilot-flying (PF) and pilot not flying (PNF) resulting in the inadequate control of the aircraft.
Five Safety Recommendations were made as a result of the Investigation as follows:
- that the Nigerian CAA should ensure adequate oversight on:
(a) Adverse Weather/Windshear recognition and recovery manoeuvres as a compulsory part of the initial and recurrent simulator training of flight crew.
(b) That the simulator used for training should be a replica of the aircraft. [2010 – 005]
- that the Nigerian CAA should:
(a) ensure that same instructor does not conduct any training and at the same time be the check airman.
(b) increase the monitoring of the quality and content of flight crew training. [2010 – 006]
- that the Nigerian CAA should ensure that NIMET expedite actions on the completion of the on-going installation of low level windshear alert systems (LLWAS) at all airports to enhance the quality of weather information obtained. [2010 – 007]
- that the Nigerian CAA should ensure that Operators’ Operations Manual/Standard Operating Procedures (SOP), which guide crew decisions in times of adverse weather and potentially hazardous atmospheric conditions, be designed to be explicit to the crew before such manuals are approved. [2010 – 008]
- that the Nigerian CAA should ensure improvement in the procedure for screening and authentication of foreign licences of personnel before such licenses are re-validated. Training organisations should also be verified and approved by the Authority. [2010 – 009]
The Final Report was published in February 2013.