An Bulgarian Air Charter McDonnell Douglas MD-82, registration LZ-LDM performing flight 1T-8115 from Catania (Italy) to Lourdes (France) with 136 passengers and 6 crew, was on an ILS approach to Tarbes-Lourdes-Pyrennees Airport's runway 20, the first officer (39, CPL, 2000 hours total, 1200 hours on type) was pilot flying, the captain (61, ATPL, 24,200 hours total, 6,100 hours on type) was pilot monitoring. The approach was fully stabilized, at 470 feet AGL the first officer disengaged the autopilot but kept autothrust active in SPEED mode maintaining 140 KIAS. Immediately after the first officer switched to manual control of the aircraft strong gusts and rain occurred, the aircraft began to drift left off both localizer and below the glideslope. The captain took control of the aircraft, corrected with a right bank and increased pitch, however, despite autothrust the aircraft continued to descend below the glide. Descending through 100 feet AGL the aircraft was completely out of all parameters for a stabilized approach, significantly below the glide, however, the captain did not call for a go around. Descending through 85 feet the captain disengaged autothrust. At a height of 58 feet the captain increased the pitch from about 4 to 11 degrees and initiated a go around, however, without adjusting engine thrust or activating TOGA, at that point the aircraft was 480 meters before the runway threshold at a height of 40+/-5 feet. The aircraft flew parallel to the ground for about 10 seconds, crossed the runway threshold at 37 feet AGL and 129 KIAS. The first officer, growing increasingly concerned, offered a call "GO AROUND". About 5 seconds later, about 350 meters past the runway threshold, the captain ordered "Go Around" and pressed the TOGA button, but did not notice that autothrust was still off and did not push the thrust levers into the position for Go Around. The aircraft travelled a further 830 meters parallel to the runway with minimal engine thrust nearing angles of attack close to stall. The first officer also did not notice the thruttle levers did not move and thus did not assist to take the engines into TOGA power. The aircraft began to slightly climb, the flaps were reduced from 40 to 11 degrees in one selection, the landing gear was retracted, at 88 feet AGL and 118 KIAS the target altitude for the go around was armed, the target speed selected to 180 KIAS and the spoilers disarmed. The speed reached a minimum of 116 KIAS at a pitch of 15 degrees nose up, the aircraft began to descend again. While disarming the spoilers the first officer noticed the thrust levers were not in the TOGA position, informed the captain and was instructed to set TOGA. At 71 feet AGL and 119 KIAS the thrust levers were aggresively pushed forward, the engines accelerated from about EPR 1.3 to EPR 2.04 (left) and 2.14 (right). At 50 feet AGL, 124 KIAS and 20 degrees nose up the aircraft began to climb again, speed increased and pitch/angle of attack reduced. The aircraft had travelled a total of 1680 meters without sufficient thrust at critical angles of attack. At 340 feet AGL the engine thrust was reduced to CLIMB power, the aircraft climbed out to safety and diverted to their alternate airfield Toulouse (France), where the aircraft landed without further incident. The captain did not report the occurrence.
The Bulgarian AAIB released their final report concluding the probable causes of the serious incident were:
On the grounds of the analysis made the Commission points out that the serious accident is the result of the following cause:
Pilots mistakes in crew coordination and in flight technology in bad weather conditions during the landing approach and the go-around procedures at the Tarbes-Lourdes-Pyrnes Airport, France.
The AAIB reported the BEA delegated the investigation to Bulgaria's AAIB, which was accepted. The BEA had been notified by Lourdes Air Traffic Controllers who "were terrified by the approach and the things, which happened, expecting the plane to crash at any moment."
Test and Research revealed the aircraft came very close to a "deep stall" but barely did not enter. The AAIB wrote with reference to the phenomenon "deep stall": "The Commission can assume with sufficient probability that the airplane was close to the first phase of this phenomenon, but this limit was not reached with the MD-82 airplane at the LDE Airport. Retracting the flaps from 40 to 11 led for a short time to reducing the drag, but, at the same time, reducing the surface of the wing at a critical moment, partially retracting the slats, further increasing the angle of attack to preserve the horizontal flight, as a result the drag increased again without the necessary thrust to compensate the resistance together with the A/C weight. At this point, the aircraft reached the limit of the wake almost all over the wing but did not pass it. This is evident from the DFDR where the retracting of flaps was accompanied by an altitude change from 33 to 107ft, then the aircraft again lost height, increased the pitch and went down to 50ft."
The AAIB analysed that all systems of the aircraft were working normally. Unfavourable weather conditions, while "the co-pilot failed to correct the deviation in the course and glide in due time" did not cause the prolonged flight in critical attitude. The crew however did not notice that the engines had not accelerated to TOGA.
The AAIB thus wrote in their analysis:
The Commission assesses the crew actions as inadequate to the procedures of the AO Bulgarian Air Charter and considers that with these actions, the flight crew contributed to the development of the situation to a critical safety hazard, such as:
1.Under the conditions of a sudden change of weather - heavy rain and gusty wind, which led to the destabilization of the approach, the A/C crew did not make a timely decision to Go-around.
2. When completing the Go-around procedure, PIC as PF, whose attention was focused on bringing the aircraft to the runway central line and the very landing, did not put the engines in TOGA mode. The co-pilot as PNF, did not control the position of the throttle, the thrust mode and the speed, and did not promptly alert the PF that they had reached critical values.
3. The flight crew was under severe stress due to the extremely unfavorable meteorological situation and the unexpected deviation from the localizer and glide path.