SERVICE LETTER Commercial Aviation Services

FLEET SUPPORT ENGINEERING BOEING COMMERCIAL AIRPLANES P.O. BOX 3707 SEATTLE WASHINGTON 98124-2207

737-SL-52-046

ATA: 5249-00 14 April 2009

SUBJECT: AUXILIARY POWER UNIT (APU) ACCESS DOOR SKIN LATCH

CUTOUTS MODEL: 737-600 to 900 Series

APPLICABILITY: All 737-600 to 900 airplanes between airplane Line Position 1275 and

airplane Line Position 2490. REFERENCE: 737 NDT Manual Part 6, 51-00-00 Figure 4 or Figure 23

SUMMARY:

The purpose of this service letter is to inform operators that the subject Auxiliary Power Unit (APU) access door latch cutout corner radii in the 148A6375-7 APU door skin do not meet Boeing drawing requirements.

BACKGROUND:

During production inspections, sharp corners were found to exist in the three latch cutouts on the subject door skin where the drawing requires a 0.127-0.133 inch corner radius. The 148A6375-7 APU door skin is used on both the 148A6350-61 and 148A6350-64 APU door assemblies.

A structural review of the condition noted that the latch cutouts are outside of the pressurized fuselage area and the stress levels around the cutouts are low enough that the discrepant condition would not cause an adverse impact to the fuselage structure. However, in order to reduce the potential for any future maintenance actions, Boeing suggests that the inspection / rework noted below be accomplished at a convenient maintenance opportunity.

BOEING ACTION:

Boeing has initiated a quality investigation and corrective action to ensure that the drawing required radii are installed on future assemblies.

737-SL-52-046

14 April 2009 Page 2 of 2

SUGGESTED OPERATOR ACTION:

We recommend that operators of the above affected airplanes inspect the noted latch cutout corners at the next convenient maintenance opportunity. Verify that no cracks exist per the reference a) High Frequency Eddy Current (HFEC) inspection method at the noted cutout corners. If any cracks are found, contact Boeing for further instructions. If no cracks are found, the corners should be rounded with a circular file to a 0.125 inch minimum radius. Maintain a surface finish of 125AA or smoother and re-protect the reworked area in accordance with the related airplane Structural Repair Manual (SRM).

ESTIMATED LABOR HOURS:

An estimated 0.2 labor hour is required to inspect the corner radii. If necessary, an additional 1.8 labor hours is required to correct the noted condition.

WARRANTY INFORMATION:

Boeing warranty remedies are available for 737 airplanes in warranty as of June 3, 2008. For inspection labor hour reimbursement for airplanes in warranty as of that date, send a claim to Boeing Warranty & Product Assurance Contracts. If the condition described in this service letter is found during the inspection for airplanes in warranty as of that date and additional labor hours are required, send a claim to Boeing Warranty & Product Assurance Contracts.

MWS:cmm