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20100420032199A

Accident · Substantial damage
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FAA accident report · Yakovlev/Wi YAK 3UPW · Half Moon Bay, CA · April 20, 2010

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Date
April 20, 2010 · 12:00 local
Place
Half Moon Bay, CA
Airport
Half Moon Bay
Phase of flight
Landing: Rollout
Operating rules
General operating rules (Part 91)
Damage
Substantial damage
Aircraft
N153U
Reported as
Yakovlev/Wi YAK 3UPW
Reported engine
Pratt & Whitney R-1830 series
People aboard
1
Fatal injuries
0
Other injuries
0
Pilot’s flight hours
0 total0 in this make and model0 in the last 90 days

From the FAA’s Accident/Incident Data System (AIDS), through its Aviation Safety Information Portal, as reported. The NTSB investigates accidents separately, and its record of an accident is the fuller one. The aircraft is matched to the registry by N-number and event date, checked against the reported make and model; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.

What happened

The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.

This accident was reopened with a new NTSB number. See previous report A-WP-27-10-010. NTSB provided funding for left main landing gear tear down analysis. The tear down was accomplished on 04/28/2010, following are the results. Mechanic statement:I removed the left main landing gear actuator from privacy data omitted yak 3.using shock air, operation of the actuator appeared to be normal. There were no internal or external leaks. After disassembling theactuator, I found some dirt contamination in the down lock ball track. The steel down lock balls were also corroded. Down line air pressurenormally forces the balls into the track to lock the actuator in thedown position. The dirt contamination could have entered the systemthrough the on-board air pump. In summary I believe a combination ofdirt in the down lock track, corroded down lock balls, low down lockpressure and perhaps a slight side load on landing caused the gear tocollapse. FAA observation:actuator was contaminated with water and dirt was noted in the ball lock track. The ball locks showed evidence of corrosion and one ball had separated from it keeper.

As the FAA filed it

THIS ACCIDENT WAS REOPENED WITH A NEW NTSB NUMBER. SEE PREVIOUS REPORT A-WP-27-10-010. NTSB PROVIDED FUNDING FOR LEFT MAIN LANDING GEAR TEAR DOWN ANALYSIS. THE TEAR DOWN WAS ACCOMPLISHED ON 04/28/2010, FOLLOWING ARE THE RESULTS. MECHANIC STATEMENT:I REMOVED THE LEFT MAIN LANDING GEAR ACTUATOR FROM ^PRIVACY DATA OMITTED^ YAK 3.USING SHOCK AIR, OPERATION OF THE ACTUATOR APPEARED TO BE NORMAL.THERE WERE NO INTERNAL OR EXTERNAL LEAKS. AFTER DISASSEMBLING THEACTUATOR, I FOUND SOME DIRT CONTAMINATION IN THE DOWN LOCK BALL TRACK. THE STEEL DOWN LOCK BALLS WERE ALSO CORRODED. DOWN LINE AIR PRESSURENORMALLY FORCES THE BALLS INTO THE TRACK TO LOCK THE ACTUATOR IN THEDOWN POSITION. THE DIRT CONTAMINATION COULD HAVE ENTERED THE SYSTEMTHROUGH THE ON-BOARD AIR PUMP. IN SUMMARY I BELIEVE A COMBINATION OFDIRT IN THE DOWN LOCK TRACK, CORRODED DOWN LOCK BALLS, LOW DOWN LOCKPRESSURE AND PERHAPS A SLIGHT SIDE LOAD ON LANDING CAUSED THE GEAR TOCOLLAPSE. FAA OBSERVATION:ACTUATOR WAS CONTAMINATED WITH WATER AND DIRT WAS NOTED IN THE BALL LOCK TRACK. THE BALL LOCKS SHOWED EVIDENCE OF CORROSION AND ONE BALL HAD SEPARATED FROM IT KEEPER.