The FAA and EASA have issued safety bulletins warning operators of certain Hawker jets that duct and sleeve clamps on the air-cycle machine and water separator can become loose and lead to a potential loss of cabin pressure. This condition potentially affects Textron Aviation Hawker 750, 800, 800 (U-125A), 800XP, 850XP, and 900XP series aircraft.
According to an FAA Special Airworthiness Information Bulletin (SAIB), the regulator has received multiple reports in recent years of sudden disconnections of air-conditioning system ducts and sleeves attached to the air-cycle machine and water separator, which can occur at both ends of the air-cycle machine’s discharge duct and immediately downstream of the water separator. Disconnections are usually accompanied by a popping sound or loud bang followed by a cabin rate of climb more than 2,000 fpm, depending on cabin altitude. FAA noted in the SAIB that in each instance reported to the agency, crews were able to safely land their airplanes.
Improper re-torquing of the clamps following parts replacement or other maintenance is believed to be behind the disconnections. Textron Aviation is updating sections of the maintenance manual to bring attention to the correct torque requirements for the clamps. The FAA recommends not to under- or over-tighten the clamps beyond Textron’s specifications.
For out-of-phase inspections mentioned in the aircraft flexible maintenance schedule, the FAA recommends that maintainers check for the correct torque loading of the clamps after any disturbance of the air-conditioning ducts or rubber sleeves as close as possible to the lower 50-hour limit.