SPECIAL AIRWORTHINESS INFORMATION BULLETIN
Aircraft Certification Service
Washington, DC
U.S. Department of Transportation
Federal Aviation Administration
CE-20-10

April 30, 2020

This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin alerts owners, operators, maintenance technicians, and inspectors of an airworthiness concern, specifically for the potential of loss of cabin pressure on (Textron Aviation Inc.) Hawker Models 750, 800, 800 (U-125A), 800XP, 850XP and 900XP series airplanes.

At this time, the Federal Aviation Administration (FAA) has determined that this airworthiness concern is not an unsafe condition that would warrant airworthiness directive action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.

Background

The FAA received multiple reports over the last several years through the Service Difficulty Reporting (SDR) system of sudden disconnections of air conditioning system ducts and sleeves attached to the air cycle machine and water separator. These disconnections can occur at both ends of the air cycle machine discharge duct and immediately downstream of the water separator. The disconnections are typically accompanied by a popping sound or loud bang being heard and are followed by a cabin rate of climb greater than 2,000 feet per minute, depending on cabin altitude. In all cases, the crew was able to land the airplane safely.

It is suspected that clamps securing the rubber coupling sleeves to the ducts either had become loose or were improperly torqued after installation or maintenance. Loosening of the clamps can sometimes occur in operation after parts replacement or other maintenance activities have occurred that require re-torqueing of the clamps. The duct/clamp configuration is common among the models of airplanes listed.

Recommendations

The FAA recommends paying close attention to the security of the clamps connecting the rubber sleeves to the air cycle machine and water separator as detailed below:
  1. Observe the hose clamp torque requirements identified in the applicable Aircraft Maintenance Manual, Sections 21-10-15, 21-10-87 and 21-10-95. Do not under tighten or over tighten these clamps.
Note: Textron Aviation is updating the sections of the maintenance manual to call attention to the proper torque requirements of these clamps.
  1. In accordance with the Out of Phase Inspections provided in the Aircraft Flexible Maintenance Schedule: After any disturbance of the noted air conditioning ducts or rubber sleeves, check the duct joint clamps for the correct torque loading. Perform this check as close as practicable to the lower 50-hour limit rather than the allowed 300-hour limit.
For Further Information Contact

David Enns, Aerospace Engineer, 1801 Airport Road, Wichita, KS 67209; phone: (316) 946-4147; fax: (316) 946-4107; e-mail: david.enns@faa.gov.

For Related Service Information Contact

Textron Aviation Customer Service, P.O. Box 7706, Wichita, KS 67277, U.S.A.; phone: (316) 517-5800; fax: (316) 517-7271.