US investigators probing a landing excursion which badly damaged an IAI 1125 Astra business jet have been unable to explain the apparent loss of braking effectiveness during the roll-out.
The Astra had touched down on the 5,000ft runway 16 at Chicago Executive airport on 21 August 2023. Weather conditions were good and the runway was dry.
Its pilot told the National Transportation Safety Board that he applied brakes and deployed the thrust-reversers after landing in the touchdown zone.
But the inquiry believes reverse-thrust was not engaged, contradicting the testimony from the crew.
Investigators concluded that the thrust reversers were not deployed based on surveillance video and analysis of logic conditions from the digital electronic engine control. The inquiry was unable, however, to determine whether the jet’s airbrakes – two on each wing – were deployed or stowed during the roll-out.
The aircraft was not fitted with a flight-data recorder and cockpit-voice recorder information was unavailable, having been overwritten during post-accident maintenance work.
After touchdown the pilot remarked that the brakes “were not grabbing” and advised the co-pilot, who applied his brakes with no effect, according to the investigation.
The pilot used the emergency brake handle in a bid to slow the aircraft and attempted to vacate the runway via a left-hand 45° taxiway, believing it would provide additional stopping distance.
But the jet skidded to the right of the taxiway, veering onto grass, sustaining a landing-gear collapse and substantial damage to the right wing spar. Neither pilot, the only occupants, was injured.
Examination of the aircraft showed no evidence of mechanical malfunction of the brakes or any other systems. Tyre skid marks indicated heavy wheel braking on the runway and taxiway.
Investigators calculated the landing distance, with airbrakes and anti-skid active, at 2,525ft, and some 4,200ft – exceeding the runway length – with neither. As the runway was dry, there was no distance credit from using reverse thrust.
Simulations attempted to determine whether the airbrakes were deployed during the landing. But the simulations found that – even if the airbrakes were deployed – the wheel-braking friction coefficient would need to have halved from its expected value to match the aircraft’s trajectory data.
“Consequently, the lack of deceleration during the accident could not be explained solely by postulating that the airbrakes were stowed,” says the inquiry. It adds that it has been unable to determine the reason for the crew’s reported loss of braking effectiveness during the landing.