Learjet 40 aircraft and Learjet 45 aircraft Bleed Air Issues: Part II—Leaks

November 2015

This is the continuation of the Bleed Air issues that some Learjet 40* aircraft & Learjet 45* aircraft operators have been experiencing with various ongoing intermittent Bleed Air issues. Some are false indications, some are actual leaks. Some of these are more noticeable during hot weather operations with Learjet 45 aircraft equipped with APUs, but are not limited to those aircraft. There has been quite a bit of work done to resolve these issues.

In Part I (Learjet 40 aircraft/Learjet 45 aircraft Bleed Air Issues: Part I-Indicating), I addressed the indication issues. So now I will move on to leaks. I have listed the Service Bulletins that address the leaks below to start.

1. SB 45-30-04/ SB 40-30-01 (Recommended)
   • Inspection/ Replacement of PerkinElmer Bleed Air Couplings in the Anti-Ice System
   • This is to check P/Ns of some defective couplings and replace as required.
2. Service Bulletin (SB) 45-21-20/ SB 40-21-05 (Recommended)
   • Inspection/ Replacement of PerkinElmer Bleed Air Couplings in the Environmental Control System
   • This is to check P/Ns of some defective couplings and replace as required.
3. SB 45-36-2 (Optional) Replacement of the HP Bleed Air Manifold on early 45s that had a 300 hour Inspection for cracked attachment flange welds. This is usually a part replacement upon failure.
4. SB 45-36-7/ SB 40-36-03/ SB 75-36-01/ SB 70-36-01 (Optional) Replacement of the HP Ducts (RH & LH MUST be replaced together) with an improved duct. SBs 45-78-11 & 45-36-8/ 40-78-05 & 40-36-04 must be complied with prior or in conjunction with incorporation of this SB. This SB is usually done after ALL other SBs have been complied with and there are still leaks in the HP duct.
5. SBA 45-49-8 (Alert) Inspection of the APU Bleed Air Duct Boot Attachment. Hopefully this is P/C/W since it is an Alert SB. This is to inspect for separation of the APU Duct Boot from the APU Primary Fire Box. This is corrected by SB 45-49-9.
   • SB 45-49-9 (Recommended) Modification of the APU Bleed Air Duct Boot Attachment. This improves the attachment of the APU Bleed Air Duct Boot Duct to the APU Fire Box.
6. SB 45-78-5 (Recommended) Improvement of the Engine Beam Firewall Seal. This SB re-works the RTV Seal around the aft engine mount area.
7. SB 45-78-10/ SB 40-78-04/ SB 75-78-03/ SB 70-78-03 (Optional) Aft Engine Mount Firewall Pan Assembly and Seal Replacement. This is another SB to improve the seal around the Aft Engine Mount to prevent hot bypass air from entering the pylon.
8. SB 45-78-11/ SB 40-78-05/ 75-78-02/ SB 70-78-02 (Optional) High Pressure Pylon Duct Seal and Bumper Plate Replacement. This SB improves the seal around the HP Duct through the Service Island. This also incorporates improved Bumper Plates and clamping to reduce movement of the HP duct, which in turns reduces the wear on the internal seals of the duct flex joints.

To summarize, there has been a lot of hard work and improvement to reduce the number of Bleed Air issues (either false indications or actual leaks) and if you are experiencing any Bleed Air Leak or indication issues, please verify the compliance of these Service Bulletins to improve the reliability of your aircraft.

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