Learjet 31A AHRS Document Errors

September 2011

Recently, I have experienced an increase in the number of inquiries about the AHRS system in the Learjet 31A. Between Service Bulletin (SB) 31-34-9, the Illustrated Parts Catalog (IPC) 34-24-11 and the Aircraft Maintenance Manual (AMM) 34-28-00, there are numerous errors.

The facts are as follows:

Learjet 31-035 thru -184

• Came from the factory with LCR-88s
• P/N 065-0147-02, item 5 in the IPC 34-24-11
• These aircraft can be modified per SB 31-34-9 to LCR-100s
• P/N 145130-7000
• This P/N is not listed in the IPC 34-24-11
• This is the only way these S/Ns can have LCR-100s installed

Please note:
This Service Bulletin is NEITHER APPLICABLE NOR APPROVED for EASA Certified Aircraft.

Learjet 31-185 & Subsequent

• Came from the factory with LCR-93s
• Can have P/N 065-00185-0101 or alternate P/N 142185-3101
• Item 7 and 7F respectively in the IPC 34-24-11
• That is ALL that can be installed in these aircraft at this time
• There is no current certification path to install LCR-100s in these aircraft at this time

FYI, the Compass Swing procedure in the MM is incorrect also in regards to the effectivities do not address SB 31-34-9. There is no callout if LCR-100s have been installed.

Ongoing Support

With this being said, LCR-88s will only be supported for repairs as long as the current inventory of parts exists. Once these parts are depleted, there will be no repairs for LCR-88s. At that point, the only option currently available is to comply with Service Bulletin 31-34-9.

LCR-93s are being supported for repairs. This is why there is no current certification plan to install the LCR-100s in aircraft that currently have the LCR-93s installed.

LCR-100s are still being produced and repairs are still currently being supported.