AD 2021-23-11 Airworthiness Directives; Learjet Inc. Airplanes

This AD applies to Learjet Inc. Model 45 (Learjet 40), Model 45 (Learjet 45), Model 45 (Learjet 70), and Model 45 (Learjet 75) airplanes, serial numbers 45-002 through 45-556 and 45-2001 through 45-2146, certificated in any category.

Comply with this AD within the compliance times specified, unless already done.

Within 60 days after the effective date of this AD, report the following information, where available, to the Wichita ACO Branch via email at thomas.teplik@faa.gov and Wichita-COS@faa.gov; or by mail to Wichita ACO Branch, FAA, Attn: Thomas Teplik, 1801 S. Airport Road, Room 100, Wichita, KS 67209. (1) Name of the owner; the address of the owner; name of the organization doing the actions required by this AD; the date the actions were completed; the name of the person submitting the report; the address, telephone number, and email of the person submitting the report. (2) The fan vibration levels that have been recorded in the airplane and engine maintenance records since November 1, 2019. Include the airplane and engine serial numbers. (3) The date of each vibration level recorded and the associated hours time-in-service (TIS) for the airplane and each engine. (4) For each fan vibration level reported, include: (i) Whether molybdenum coating for the fan was applied per Temporary Revision 72-494, dated August 15, 2017 (or as subsequently incorporated into the engine's Inspection/Repair Manual TFE731 (ATA Number 72-IR-02)). (ii) If molybdenum coating was applied using a different process than Temporary Revision 72-494, dated August 15, 2017 (or as subsequently incorporated into the engine's Inspection/Repair Manual TFE731 (ATA Number 72-IR-02)), report the process by which the molybdenum coating was applied and the revision level of the document defining the application process for the molybdenum coating. Note 1 to paragraph (g)(4): Temporary Revision 72-494, dated August 15, 2017, specifies applying a dry film lubricant on the mating surfaces of the fan hub and the fan blades. The lubricating solid for this dry film lubricant is molybdenum disulfide, which is referred to in this AD as molybdenum coating. (5) For each fan vibration level reported, the fan hub serial number and hours TIS for this fan hub. (6) Installation date and service bulletin (SB) revision level for the installation of the bracket assembly with fuel flow meter and hose if installed before the effective date of this AD. (7) Any failures of the bracket assembly with fuel flow meter and hose installed in accordance with any SB listed in paragraph (h) of this AD or any prior revision of these SBs. (8) Installation date and SB revision level used for installation of the fuel control screws within the engine fuel control in accordance with Honeywell SB TFE731-73-5146. (9) Any failures of fuel control screws after compliance with Honeywell SB TFE731-73-5146.

This AD was prompted by a report of a fuel leak due to a cracked fuel line between the engine fuel control and the engine fuel flow meter. The FAA is issuing this AD to prevent cracking and failures. The unsafe condition, if not addressed, could result in an engine installation fire, which could progress to an uncontrolled fire and consequent loss of control of the airplane.

None.