Gear
Failure
What happens when you don't
get "three green"
On December 16th, 2002 I was crewing a Bearskin Airlines Beech 99 aircraft that had a major failure of the nose gear hydraulic actuator resulting in a gear up landing at Sioux Lookout airport in Ontario.
Below is a copy of the occurrence report filed with the company the following day.
The aircraft was repaired and flying about 10 days after the accident, the only significant (and unavoidable) damage being to the propellers, power turbine section of both PT6 engines, and the fiberglass nose cone & forward bulkhead which were worn through from sliding down the runway. These repairs, though costly, were relatively simple and carried out quickly.
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WHAT DID THE COMPANY SAY? |
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Within a week of the occurrence the company publicly responded with a letter commending everybody involved. To see what they said, click here. |
The inability to extend the nose gear was caused by a one inch hole which blew out of the end of the nose gear hydraulic actuator. This allowed hydraulic fluid (from both the main and backup systems) to be pumped overboard resulting in a lack of pressure with which to extend the gear. The failure mode appears to be a weakness of this specific type of hydraulic ram as an identical failure occurred on the same aircraft the previous year (in that case, fortunately, the failure occurred with the gear in the down position). Post failure inspection also shows that the wall thickness at the critical point is relatively thin. Before putting the aircraft back into service, the company acquired an updated hydraulic actuator which will hopefully prevent another similar failure.
Maintenance personnel also believe that the hydraulic pressure of the system on this specific aircraft may be set too high resulting in excessive stresses on system components (and hence the two failures). Since there is no pressure gauge in the cockpit, it is impossible for flight crew to verify this -- it is purely a maintenance function.
The professional manner in which the emergency was handled was reflected in the calmness of the passengers throughout the occurrence, the minimal damage to the aircraft, and the lack of even minor injuries.
Enjoy the report.
Occurrence Report
Occurrence Date: Dec 16, 2002, 0245Z, Sioux Lookout, ON (CYXL)
PIC: L. Martel #AA340930
SIC: C. Holmes #AA406124
Aircraft: C-GFQC
YXL Wx: VFR; ceiling 1200, vis approx 10sm, wind 120 @ 5-10
Flight: Bearskin 327
Report submitted by C. Holmes
I was the PF on the leg from Round Lake (ZRJ) to Cat Lake (YAC) while Lawrence Martel, the captain, was the PNF.
Departing ZRJ, when selecting gear up, the captain noticed the HYD LOW light illuminate. The gear locked in the up position, the in transit lights extinguished along with the HYD LOW light. No further consideration was given at the time.
On final approach into YAC I called for gear down. The captain actuated the lever but received no indication of operation (no in transit lights, no downlock lights, and the DO NOT REVERSE annunciator did not illuminate. The captain recycled the gear handle without any indication. I checked the CB panel and found the GEAR CONT CB popped. When reset (with the gear handle down), the hydraulic motor began running (the DO NOT REVERSE annunciator illuminated) but no in transit or down lock lights illuminated. When it became evident that the gear was not extending the CB was pulled to stop the hydraulic motor from running and the gear handle returned to the RETRACT position. We initiated the overshoot at YAC and continued to YXL. Maintenance and dispatch were notified of the situation as soon as we were in radio range and trouble-shooting began. 20nm from YXL we ran through the manual extension checklist. After pumping the manual hyd lever for 10 minutes, the in transit lights illuminated, but no downlock lights. We tried resetting the GEAR CONT CB again which resulted in a green downlocked indication on both main gear. However, the in transit lights remained illuminated and the nose gear downlock remained extinguished. Now knowing that we had a potentially serious problem, ATC was notified of the situation. I handed control of the aircraft to the captain. We performed a low pass over the airport so that maintenance personnel could visually confirm the position of the nose gear. It was noted that the nose gear was only extended to a 45 degree angle. At this point we declared an emergency with ATC. Maintenance suggested we try performing some high-G maneuvers in an attempt to fully extend the nosewheel. While we circled, I went back into the passenger cabin to brief them on the situation, demonstrate a safe seating posture, and ensure seatbelts and cabin bags were secure. The captain then executed a dive/pullout maneuver but was unable to attain downlock indication on the nose gear. Another low pass over the airport confirmed the nose gear still was not extended. The captain and I then briefed the landing and I subsequently briefed the passengers. We touched down gently on YXL RWY 16. When the main wheels were firmly down, I moved the condition levers to cut-off and pulled the fire T-Handles while the captain held the aircraft nose in a level attitude until losing elevator authority. The nose fell slowly to the runway, the wind milling propellers struck the pavement, and we came to a halt at 0245Z. The emergency crews responded immediately by foaming the nose of the aircraft as a precautionary measure. The captain cut electrical power and I briefed the passengers to remain seated. When it was determined that the aircraft was secure and would not tip on its tail, we evacuated the passengers through the left hand over-wing exit. There were no injuries and the passengers remained calm at all times.