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Stuck in the mud

Wed, Jan 30, 2008 — David Evans

Briefs

A flight by a double deck Airbus A380 had to be abandoned the evening of 10 January after it rolled off a taxiway at Singapore. The 446 passengers on Singapore Airways flight SQ221 were unhurt and were switched to a B747 while the A380 was checked for damage.

This is the first known incident involving the new super jumbo in revenue service.

The A380 had not yet started its engines and was being pushed back by a ground tractor. The tug had a brake failure due to a massive hydraulic leak, and the airplane, with rearward momentum, rolled off the taxiway onto the grass.

“The damage is very limited; it’s superficial in the sense that there is possibly damage to the tires,” said Singapore Airways official Stephen Forshaw.

It is interesting that the pilots were not able to brake the airplane before it rolled off the taxiway, but not because the airplane’s engines were not started, nor because the airplane would therefore have lacked hydraulic power to its brakes. Some auxiliary braking systems can run courtesy of a battery direct or via APU-powered bus. It’s a little known fact that pilots are encouraged never to apply brakes while reversing unless it’s a dire emergency, as braking tends to sit the airplane on its tail. Positive thrust should always be applied first, in order to glue the nose wheels to the deck. That wasn’t an option here.

It is normal for there to be a “brake-rider” whenever an airliner is being towed – but ground crews are probably also briefed to avoid wheel braking while in rearward movement.

This incident appears at first blush to be solely in the province of a ramp operations incident.

Figure A
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Note the depth to which the tires sank into the turf.
Figure B
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Another view, again showing the extent of gouging into the soft unpaved surface.

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