Preventive Maintenance for Thrust Reversers

Preventive Maintenance for Thrust Reversers By Michael M. DiMauro March 2000 Rugged and reliable, few mechanics consider thrust reversers as a threat to the aircraft's safety. For the airlines, however, they can be a threat to other...

Translating Cowl (transcowl)
First, a general inspection of the transcowl should include checking for loose or missing or cracked rivets. Look for surface damage such as cracks, holes, dents, and delaminations. Also check for damage to the graphite C-Ring as well as the mateline of the inner and outer bondments.

Next, visually inspect the Main Air Seal for cuts, splits or punctures.

Cowl guides on the outer bondment of the transcowl have a TeflonĀ® strip bonded at the contact area to the fixed structure. Check this strip for wear, and replace cowl guides that show worn or missing Teflon. This will prevent unnecessary wear on the guide track on the hinge/latch beam. This guide track is integral to the beam, and protecting it can avoid a costly and time-consuming beam replacement or specially manufactured detail to replace the cowl guide track.

Be sure to check the transcowl T-track liners. These are the plastic liners that are in the hinge and latch beams where the transcowl T-hinge slides. Loss or severely worn liners can cause wear on the hinge beam and/or T-hinge, both costly repairs or replacements.

Also, check the bearings of the blocker door hinge blade and replace worn hinges on the blocker door and/or transcowls. Worn hinges will allow blocker doors to vibrate and may cause damage to both the doors and the transcowl.

Support Assembly

Check for cracks in the torque box actuator casting. Cracks not repaired according to OEM guidelines may cause gearboxes to become detached from the torque box.

Whenever possible, look for damage to the fire coat. Loss of firecoat can cause premature bondline failures on the sidewalls and core cowls, and should be scheduled for out of service maintenance as soon as possible.

But, as reliable and rugged as large engine reversers are, periodically they do suffer from serious failures. A significant portion of all unplanned maintenance comes from operational damage (activating wing flaps while reverser is open, striking the reverser; engine fires; runway debris, etc.). After that, the causes range from general hydraulic leaks and actuation system failure to handling damage (fork trucks, baggage carts, ladders, etc.)

The average service life of a large engine thrust reverser is in excess of 100,000 flight hours, so if properly maintained, most reversers will last through several overhaul intervals.

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