Investigators have described the extraordinary effort to control an airborne SmartLynx Airbus A320 using stabiliser trim and thrust from its badly-damaged engines, after the aircraft struck the runway with its engine pods during a failed touch-and-go exercise.
The A320 suffered elevator failure as it rolled out after touchdown at Tallinn and did not respond to side-stick rotation commands as it accelerated for take-off.
Estonian investigation authority OJK found that a brief rebound of the landing gear during the touchdown – performed without the spoilers being armed – combined with a "weakness" in a particular aspect of system logic resulted in a loss of pitch control by both spoiler elevator computers.
Seven people were on board for the series of exercises: a student pilot in the first officer's seat, an instructor in the captain's seat, plus a safety pilot and a civil aviation authority inspector in the jump-seats. Three other students were in the passenger cabin.
These three students had already undergone touch-and-go practice, and the fourth was carrying out his third touch-and-go cycle, accelerating for take-off on runway 08 with the engines at full thrust.
But the aircraft failed to respond to a rotation command from the side-stick at about 130kt. The centralised aircraft monitor showed a left and right elevator fault, and warned of manual pitch-trim only.
Although the elevators were locked at neutral, the horizontal stabiliser was slightly nose-up and the aircraft became airborne at 152kt. The instructor took control from the student and found that there was no response in pitch from the side-stick.
The inquiry says that, as aircraft reached a height of 19ft, it was 950m from the far end of the runway. Its thrust levers were retarded to 'idle', the flap setting was reduced, and the captain ordered the landing-gear retracted.
Loss of thrust meant that, after reaching 48ft, the aircraft started to descend and, with its landing-gear still in transit, the A320 struck the runway – about 200m from the end – with its engine pods, damaging the powerplants substantially.
The impact caused the jet to pitch up and it started to climb away at 6,000ft/min, pitched nearly 20° nose-up, with its right-hand engine on fire.
From the jump-seat the safety pilot remarked that the aircraft needed "manual pitch-trim only", and the crew began to control pitch, lowering the nose by turning the horizontal stabiliser's pitch-trim wheel and selecting different engine thrust settings.
The aircraft reached a maximum height of 1,590ft and entered a dive at nearly 26° nose-down – reaching 7,200ft/min and descending to 596ft – before the instructor move the thrust levers to a higher setting and trimmed the stabiliser nose-up.
OJK says multiple warnings sounded in the cockpit, including the master alarm and several terrain-awareness cautions including 'sink rate' and 'pull up' alerts.
But the instructor managed to stabilise the A320 at about 1,200ft and 155kt, using side-stick roll input and a combination of trim and thrust to handle the pitch – despite the damage to the engines.
"Do we have engines?" the instructor asked, about 1min after the runway impact, to which the safety pilot responded: "We have engine two fire."
The aircraft was not only operating in mechanical back-up mode for pitch control, following the elevator failure, it was also flying in direct law in the roll axis and alternate law in the yaw axis, with its flaps locked.
Having achieved relative stability at 1,300ft for about 30s – despite pitch varying between 8° nose-down and 16° nose-up – the crew declared an emergency and agreed to attempt a right turn for a visual approach back to the opposite-direction runway 26. The safety pilot took the first officer's seat, with the student and the inspector retreating to the cabin.
Tower controllers were informed of the decision and asked to summon the emergency services.
Although the safety pilot suggested reducing power from the fire-hit right-hand engine, the instructor chose instead to maintain thrust and keep the engine operating as long as possible, given the deterioration in other flight controls. The engine began to fail and shut down about 30s later.
The crew extended the aircraft's landing-gear and set landing flaps.
About 20s after the right-hand engine shut down, the left-hand engine similarly failed, the result of seizure from low oil pressure following impact damage to the accessory gearbox. Several electrical systems ceased to function and the ram-air turbine deployed automatically.
"Gear is down, we don't have engines," the safety pilot stated, and the aircraft glided towards the runway, touching down heavily about 150m before the threshold, bursting all of its tyres before coming to a halt close to the left edge of the runway. The damage resulted in the A320's being written off but only minor injuries were suffered by those on board.
OJK credits the crew with having followed the "golden rule" – aviate, navigate, communicate – during the accident, on 28 February last year. It says the safety pilot's initiative, the quick turn-back, and the decision to keep the engines running, enabled those in the cockpit to keep the jet under control and land without casualties.