Lion Air investigation finds adverse conditions and non-simultaneous reverser deployment contributed to accident
Indonesian investigators probing the fatal Lion Air Boeing MD-82 landing overrun at Solo in November have revealed that wet surface conditions, a strong tailwind and the non-simultaneous deployment of thrust reversers contributed to the twinjet's sliding off the runway.
Twenty-six of the 163 people on board were killed after the MD-82 crashed into a fence and a set of airport navigation equipment, severely damaging the forward fuselage.
Following a normal approach on 30 November, flight LNI538 touched down about 500m (1,640ft) past the threshold of Solo airport's runway 26, leaving about 2,000m for the aircraft to come to a halt. But thunderstorms and heavy rain had left the runway slippery and the MD-82 aquaplaned as it attempted to slow down.
Flight-data recorder information showed that the tailwind at the time was around 13kt (24km/h) even though the weather information received by the flightcrew indicated a windspeed of about half that figure.
National Transport Safety Commission (NTSC) investigators in Indonesia say that the spoilers deployed immediately, but only for 2s. The crew, they add, were unaware of this because they were concentrating on the braking.
"At the time of the landing roll, the aircraft experienced a change in direction - a swing to the left and right - caused by the existence of pools of water on the surface of the runway that led to aquaplaning," says the commission. It adds that the right-hand thrust reverser deployed 8s later than the left-hand reverser. The investigation report says that the asymmetry exacerbated the difficulties in maintaining the aircraft's direction.
"The pilot tried to correct the swing so that the aircraft did not leave the side of the runway," it says. "These efforts...were successful, but reduced braking."
After failing to stop, the MD-82 overran the end of the runway, striking the localiser antenna about 140m from the runway end. The pilot had attempted instinctively to lift the nose of the jet before impact. Such was the ineffectiveness of the braking and deceleration that the aircraft's speed had only slowed to 87kt at the time of impact, compared with 138kt at touchdown.
Among several recommendations to the Indonesian transport ministry, the investigators say that airports should periodically take measurements to check that runway friction is adequate and obtain data on braking in wet conditions. They have also recommended that weather-monitoring equipment be checked so that pilots receive up-to-date information on windspeeds.
DAVID KAMINSKI-MORROW / LONDON
Source: Flight International
