SilkAir jet lost part of its tail before crashing

CRASH investigators acknowledged yesterday that the SilkAir jet lost part of its tail before it nose-dived into the Musi River.

Six pieces, including the horizontal stabilisers which control the plane’s up-and-down movement, were found on land nearly 7 km away.

This lends weight to the theory that faults in the tail brought down the jet.

Sources close to the investigation believe that rivets could have been missing from the horizontal stabilisers and that this led to the crash. “It is a possibility and we are looking into that,” said one source. He said: “What is clear for now is that we found pieces of the plane’s tail on land to indicate that they dropped off in mid-air.”

Exactly three weeks since Flight MI 185 ended in the Musi River, more than half the wreckage has been found, including theflight data recorder and cockpit voice recorder now being analysed in the US.

The tail fragments found 6.8 km from the site included the horizontal stabilisers which make up the crosspiece of the tail, below the upright fin that houses the rudder.

If these stabilisers had rivets or fasteners missing, it could have resulted in catastrophic loss of control.

The US Flight Aviation Administration, which has ordered an immediate inspection of the tail sections of 211 late-model 737s, said no cause had been pinpointed for the crash but that 26 fasteners in all had been found missing from the right horizontal stabiliser.

One bolt might also have been missing from a hinge on the elevator of the aircraft rear’s small wing.

But pilots wondered how this could bring an aircraft down since the missing rivets, each slightly smaller than a 5-cent coin,would be only a fraction of the hundreds on the stabilisers. It is unlikely this would cause them to dislodge.

The investigators said they were still looking for the rivets. But one source acknowledged: “It is like looking for a needle in a haystack.”

Meanwhile, SilkAir, which checked the rivets of all its five B737s on Thursday night said “everything is in order”.

A Washington Post report this week said crash forces, vibration or flutter, in flight, could have made the rivets pop out. Or parts could have worked loose or jammed in flight.

One theory is that the jet lost its horizontal stabilisers at cruising altitude and spiralled down out of control at 960 kmh and into the river at an 80 degree angle. The debris recovered indicated it disintegrated on impact.

Larger pieces found on land and traces of debris along a 7-km stretch of the river’s eastern bank probably fell off before the crash. The right wing was found 4 km away, and the right wing spoiler, 3.5 km away.

An investigator said the focus is now on reconstructing the flight pattern to find out what happened in the jet’s final minutes.

The cockpit voice recorder was in good condition, and “we were able to recover the flight data” from the flight data recorder, said the investigator.

Late next week, the wreckage may be transferred to Jakarta or Bandung to be pieced together. “It is a very complicated process which could take up to two to three months,” he said.

Meanwhile, pilots interviewed said that an aircraft would spiral down rapidly if its tail fell off. But it was unlikely the whole tail would go unless there was extensive damage to the plane, they said.

At high speed and high altitude, this would cause an explosive decompression, sucking people and even seats out. It would damage the horizontal stabilisers and jam them in a nose-dive position, causing loss of control.

If there is extensive damage to the tail, or if a wing fell off, it would cause the plane to plunge.