History of Flight
On August 21, 2023, about 1315 central daylight time, an Israel Aircraft Industries 1125 Westwind Astra airplane, registration N39TT, sustained substantial damage during a landing accident near Wheeling, Illinois. The flight crew, consisting of a pilot and co-pilot, were not injured. The airplane was operating under Title 14 Code of Federal Regulations Part 91 as a positioning flight.
The crew reported that after being cleared to land on runway 16 at Chicago Executive Airport, the airplane touched down within the touchdown zone. The pilot applied brakes and deployed thrust reversers, but the brakes “were not grabbing.” After releasing and reapplying brakes with no effect, the pilot informed the co-pilot of the brake failure. The co-pilot also attempted braking without success. The pilot then selected the emergency brake handle and applied emergency braking, which produced some slowing. Using the nose wheel tiller, the pilot attempted a left turn onto 45° taxiway D, expecting additional stopping distance. However, due to the airplane’s energy and momentum, it slid off the taxiway into adjacent grass, where the right main landing gear collapsed. The airplane came to rest upright. The crew reported no abnormal cockpit annunciators during the approach and landing.
Aircraft Information
The airplane was equipped with an airbrake system comprising four control surfaces (two per wing), electrically controlled and hydraulically operated. In flight, only the inboard surfaces deploy; on the ground, both inboard and outboard surfaces deploy when the ground airbrake switch is set to ON. Activation required electrical power, main system hydraulic pressure, at least one weight-on-wheel switch in ground mode, both throttle quadrant angle levers below 18°, and the ground airbrake switch set to ON. If these parameters were met, the ground airbrakes would deploy automatically upon landing.
According to the airplane flight manual, landing performance would be affected if ground airbrakes were inoperative. If all ground airbrakes were inoperative, landing distance must be increased by 30%.
Wreckage and Impact Information
Substantial damage was confirmed to the right wing spar on September 7, 2024, after which the event was classified as an accident. Prior to that confirmation, maintenance tests were conducted on the airplane and its braking system components under FAA supervision. No anomalies were found in the airbrake system (both air and ground modes) or thrust reverser tests. The cockpit switch positions at the time of the accident could not be determined. The operator reported that the flaps were found in the 40° extended position and the slats were extended.
Surveillance video showed the flaps appeared to be in the 40° extended position and that thrust reversers were not deployed during the landing sequence. The position of the airbrakes could not be determined. Tire skid marks were observed beginning on the runway and continuing onto taxiway D until the airplane departed the runway surface, but measurements were not recorded.
The anti-skid control box, anti-skid control valves, wheel speed transducers, and brake power valve were removed for examination at original equipment manufacturers. The examinations revealed no anomalies that would have caused a loss or reduction of wheel braking performance.
Landing performance calculations and simulations using ADS-B data, reported weather, and data from the onboard Honeywell N1 Digital Electronic Engine Control (DEEC) devices indicated that the deceleration during the accident landing roll was consistent with reduced deceleration or loss of anti-skid efficiency assuming full braking efforts by the flight crew immediately after touchdown. The magnitude of the deficiency depended on whether the airbrakes were stowed or deployed, but the simulations could not resolve the actual airbrake position. Even when assuming airbrakes deployed, the wheel braking friction coefficient would need to be reduced by half from expected values to match the data. Thus, the lack of deceleration could not be explained solely by stowed airbrakes.
Review of landing distance data for the approximate weather conditions and a Vref of 121 knots, at a landing weight of 17,576 lbs, indicated a dry, unfactored landing distance of 2,525 ft with anti-skid and ground airbrakes on, and about 4,200 ft with them off. There is no landing distance credit for thrust reversers on a dry runway.
Flight Recorders
The airplane was equipped with a cockpit voice recorder (CVR). Readout revealed two short segments of conversation about powering the aircraft electrically on the ground, and another segment consistent with maintenance operations, but without enough context to determine the nature or date of the conversation. The audio ended with no sounds associated with aircraft operations. Several maintenance actions occurred between the accident and CVR removal.
The operator’s general operations manual required the CVR to operate continuously from electrical power application to shutdown, with no erasure of communications from the time power was applied for flight. After an accident, the flight crew was required to preserve CVR data by pulling the CVR circuit breaker.
The airplane was not equipped with a flight data recorder, nor was it required to be.
Data from the Honeywell N1 DEECs showed both engines were operating and responding to power lever inputs throughout the flight and accident sequence. The data did not indicate a thrust reverser deployment. The DEEC logic requirements for thrust reverser deployment indication were not met, and no increases in N1, N2, power lever angle, or inter-turbine temperature were observed, which are typical indications of thrust reverser usage.