Pilots of a Lufthansa Cargo Boeing MD-11F failed to recognise the landing bounce which preceded a sequence of hard touchdowns and the destruction of the trijet at Riyadh, Saudi Arabian investigators have concluded.

As it conducted an instrument landing system approach to Runway 33L the aircraft flared at a low height for its 207t landing weight, and the MD-11 touched down with a sink rate of 780ft/min - far higher than the typical 120ft/min.

The resulting 2.1g impact caused the aircraft to bounce but the Saudi General Authority of Civil Aviation said the landing was still recoverable at this point.

But the crew did not appear to recognise the bounce, it said, and did not apply the recovery technique, which requires pilots to hold a normal landing attitude and apply thrust to control the rate of descent.

The technique specifically warns against making large forward or aft movement with the control column, because rapidly changing the pitch rate can result in nose-wheel damage or a tail strike.

After the initial touchdown the MD-11F bounced to a height of 4ft. Crucially the captain pushed the control column significantly forward, reducing the pitch. Because of main-gear spin-up, the aircraft's spoilers had also started deploying and this effectively reduced the angle of attack further.

These combined dynamics sapped the MD-11F's lift. Both pilots pulled on their control columns but the aircraft hit the runway a second time, in a flat attitude, with a sink rate of 660ft/min.

Its nose-gear rebounded from the 3g impact and this, combined with the pilots' control inputs, caused a 14° pitch-up as the MD-11F bounced a second time, to 12ft.

The captain responded by pushing the control column forward again, and then both pilots pulled back, but could not avert a third hard impact - some 4.4g, far above the design load - which ruptured the fuselage aft of the wing and severed fuel lines, sparking an intense fire.

"While the first touchdown resulted in a bounce, the landing was recoverable," said the GACA. "The severity of the subsequent touchdowns was not a consequence of the first touchdown, but primarily a result of the pitch angle during the bounces, which resulted from the actions of both flight crews on the control column."

Lufthansa had a long-established bounced-landing procedure, practised in simulators, which required the pilot to maintain 7.5° pitch and apply go-around thrust.

The GACA inquiry said the reason for the captain's contrary response to the initial touchdown - pushing the control column hard forward - was "unclear".

"One possibility is that the captain did not realise the aircraft had bounced and was attempting to de-rotate the aircraft while assuming the main gear were still on the ground," it said.

It points out that crews on certain aircraft types "may have difficulty" in perceiving a bounce, particularly because the cockpit height above the runway might remain constant, or even decrease.

Neither pilot mentioned handover of control, leading both to make inputs to their control columns and "aggravating" a serious situation, said the GACA, although it acknowledged that the alarm and confusion made the crew's reactions "somewhat easier to understand".

Both pilots survived the 27 July 2010 accident, despite the severe structural damage to the MD-11F (D-ALCQ), which veered off the left side of runway 33L and was consumed by the blaze.

Source: Air Transport Intelligence news