From Service Letter MTL-57-01

Date: July 20, 2018

Wings – Lower Forward Wing Bolt Crush Washer Inspection/Replacement

Compliance – MANDATORY: This service document must be accomplished within 200 flight hours or twelve months from the date of receipt, whichever occurs first.

A service document published by Textron Aviation may be recorded as completed in an aircraft log only when the following requirements are satisfied:

  1. The mechanic must complete all of the in-structions in the service document, including the
    intent therein.
  2. The mechanic must correctly use and install all applicable parts supplied with the service document kit. Only with written authorization from Textron Aviation can substitute parts or rebuilt parts be used to replace new parts.
  3. The mechanic or airplane owner must use the technical data in the service document only as approved and published.
  4. The mechanic or airplane owner must apply the information in the service document only to aircraft serial numbers identified in the Effectivity section of the document.
  5. The mechanic or airplane owner must use maintenance practices that are identified as acceptable standard practices in the aviation industry and governmental regulations.

No individual or corporate organization other than Textron Aviation is authorized to make or apply any changes to a Textron Aviation-issued service document or flight manual supplement without prior written consent from Textron Aviation.

Textron Aviation is not responsible for the quality of maintenance performed to comply with this document, unless the maintenance is accomplished at a Textron Aviation-owned Service Center.



Serial Numbers


F90LA-1 thru LA-225 with Kit 90-4077 and Kit 101-4024-3 installed

H90 (T44A)

LL-1 thru LL-61 with Kit 90-4077and Kit 101-4024-3 installed


U-50, U-165 and on, with Kit 90-4077 and Kit 101-4024-3 installed

65-90, 65-A90, 65-A90-1, 65-A90-4,
B90, C90, E90

All serials with Kit 90-4077 and Kit 101-65-A90-2, 65-A90-3,

99, 99A, 99A (FACH), A99,
A99A, B99

All serials with Kit 90-4077 and Kit 101-4024-3 installed

100, A100 (U-21F), A100A,
A100C, B100

All serials with Kit 90-4077 and Kit 101-4024-3 installed

Labor Hours:
For planning purposes only:

Work Phase

Labor Hours





Reason: Alternate 90-380058-1 Washer Assembly has been determined to provide premature torque indication. This could lead to cracking of the wing fitting. This washer assembly may have been installed during incorporation of Kit 101-4024-3.

Warranty: This service document is mandatory. Eligible air-planes may qualify for parts and labor coverage to the extent noted in the Labor Hours and Material Availability sections of this document.

Airplanes identified within the serial number effectivity of this service document must have active Airframe warranty coverage on the original issue date of this document and the coverage must be active on the day the work is accomplished.

As a convenience, service documents are now available online to all our customers through a simple, free-of-charge registration process. If you would like to sign up, please visit the Customer Access link at to register.

The above information may be abbreviated for space purposes. For the entire document, go to

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