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25th of February 2017, Maintenance Error, Blog #640

A Socata TB20 was on a cross-country flight from Key West (Florida, USA) to Daytona Beach (Florida, USA) under VFR regulations. During the flight the alternator warning light flashed and the pilot observed the aircraft battery began to discharge from 28 to 24 volts. ATC was contacted for a diversion to Melbourne (Florida, USA) no emergency was declared. On the approach to Melbourne (Florida, USA) as the aircraft was configured for landing, the nose landing gear failed to extend. After multiple unsuccessful attempts to lower the landing gear (Emergency Gear Procedure due to electrical failure), the pilot performed a gear-up landing.

The nose landing bay and forward fuselage, note the forward bulkhead damaged by the overextended nose landing gear (Source & © NTSB)

The gear-up landing was successful with the aircraft coming to a stop after ~700 feet, there were no injuries, and there was some damage to the airframe:

  • The propellor struck the runway

    • Engine requiring overhaul

  • Steps to wing sheared off

  • The belly of the aircraft scratched

  • Right Main Landing Gear tire flat

After the aircraft was pulled off the runway (as-is) it was lifted up.

The left main landing gear came down, the right main landing gear needed a little help to come down. The nose gear needed a lot of work to come down as it was initially stuck in the nose landing gear bay, when it came down it moved smoothly in the down and locked positions. The aircraft was then hand towed/pushed to a tie-down position near the airport hangars, where it was parked.

The over-extended nose landing gear, and flat right-hand tire (Source & © NTSB)

The National Transportation Safety Board was alerted and an inspection of the aircraft was carried out by a Federal Aviation Administration Inspector. This inspection revealed that the nose landing gear did not extend and remained in the

wheel well. Examination of the airframe revealed that the bottom forward bulkhead was damaged during the landing sequence. An examination of the nose gear assembly revealed the circlip on the nose landing gear strut was dislodged from the nose landing gear leg assembly, which allowed the strut to extend further than usual. The circlip used to retain the nose gear strut inside the nose gear assembly had paint on the outer portion of the circlip, which should have been fully set inside the groove used to keep the

circlip in place. An examination of the circlip groove revealed that it was in serviceable condition with no corrosion or other deformation within the groove. A review of the maintenance records showed that the nose strut was disassembled and repaired on July 15, 2015, and the airplane was completely repainted on April 5, 2016. Further review of the maintenance records revealed that since the disassembly of the nose gear, a total of 75 hours of flight time had accumulated since the maintenance.

According to the airplane's maintenance manual, the nose landing gear strut retaining circlip should have been fully installed in the groove. After it is installed, the landing gear should be rotated several times to confirm proper installation.

Note the circlip resting on the nose landing gear, at the red arrow (Source & © NTSB)

The NTSB concluded that the probable cause of the accident was:

Improper installation of the circlip within the nose gear strut, which resulted in the strut overextending in the wheel well and preventing the nose landing gear from extending during landing.

The NTSB report which served as the source for this report can be accessed by clicking on the .pdf file below;

25feb2017 Socata TB20 Gear Up Landing
Download PDF • 801KB

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