History of Flight
On May 17, 2011, at approximately 0645 mountain daylight time, N218YV, a Beech BE-1900D, sustained minor damage when the left main landing gear (LMLG) collapsed during landing rollout on Runway 35L at Denver International Airport (DEN), Denver, Colorado. The airline transport pilot rated captain, commercial rated first officer, and the nine passengers were not injured. The airplane was registered to Raytheon Aircraft Credit Corporation and operated by Great Lakes Aviation. An instrument flight rules flight plan was filed for Flight 5150, which originated at Pueblo Memorial Airport (PUB) about 0607 and was destined for DEN. Visual meteorological conditions prevailed.
According to the captain, during approach, the first officer called for gear extension. The captain placed the gear handle down and observed that only the “NOSE”, “RH”, and “L” annunciator lights illuminated; the “H” light for the left gear did not. The in-transit light remained on, and the gear motor ran for about 16 seconds before the gear-motor relay circuit breaker popped. The captain believed the gear was down and locked because at least one light per gear leg was illuminated. Just before touchdown, the gear unsafe warning horn sounded, but the captain did not go around. After landing, the airplane wobbled and the left main gear collapsed.
Personnel Information
The captain held an airline transport pilot rating for multi-engine land and a first-class medical issued August 24, 2010. He reported about 3,250 total hours, with 2,800 in the Beech 1900D. The first officer held a commercial pilot certificate and a first-class medical issued February 3, 2011, reporting about 950 total hours, with 85 in type.
Aircraft Information
The Beech BE-1900D has a retractable tricycle landing gear system. Extension and retraction are hydraulic, controlled by a handle with UP and DN detents. The system includes a hydraulic power pack and individual actuators. Visual indication is provided by six green lights (two per gear leg) and two red in-transit lights in the handle. The annunciator assembly uses lamp modules with part numbers; a light dam separates bulbs. The operator examined the incident airplane's annunciator assembly and found that a lamp module marked P/N 90-42292-001 with an L and R face plate was installed in the center position, but the light dam was missing, causing light from the illuminated "R" bulb to bleed over and make "L" appear lit. A search of maintenance records revealed only two bulb replacements since the airplane entered service. The operator then found 15 of 31 fleet airplanes had discrepant annunciators.
The nose landing gear (NLG) actuator had been overhauled in August 2008 after removal for a circuit breaker issue. It was reinstalled in July 2009. At the time of the incident, it had accumulated 29,533 cycles since new and 4,585 since overhaul.
Meteorological Information
Weather at DEN at 0641: wind 260° at 7 knots, visibility 10 miles, few clouds at 14,000 feet, broken at 20,000 feet, temperature 7°C, dewpoint 4°C, barometric pressure 29.70 inHg.
Wreckage and Impact Information
The airplane came to rest on the left side of the runway about 6,090 feet from the approach end. Minor damage included the removable wingtip/winglet, lower wing skin, flaps, and lower left aileron skin. Runway gouging from propeller strikes and debris were noted. The top portion of the NLG actuator end cap was found on the runway. Hydraulic fluid pooled under the NLG at the final position. Cockpit examination showed the landing gear handle down, the LANDING GEAR RELAY circuit breaker popped, flaps at 17°, and trim settings. After lifting, the LMLG fell to the down position with no evidence of failure. When powered in the hangar, all six green annunciator lights illuminated.
Testing and Research
Hawker Beechcraft reported five previous NLG actuator end cap failures. Examination of the incident end cap and a previous failed cap by an NTSB metallurgist revealed both failed in fatigue from multiple origins propagating from the inside diameter outward. The actuator was designed to Hawker Beechcraft specifications and manufactured only by APPH. During overhaul, end caps are dye penetrant inspected. The actuator drawing was revised in February 2010 to add grain direction, but this change was not related to the fatigue failures.
The LMLG actuator was functionally tested and found within limits with no pre-mishap anomalies. The LMLG drag brace and hardware also tested normally. It was concluded that when the end cap failed, system pressure decreased, most hydraulic fluid was expelled from the NLG actuator, and the pressure pulse delay to the LMLG, combined with a history of slow extension, prevented the LMLG from reaching full down and locked before pressure was lost. The failure also disabled the emergency manual extension system.
Additional Information
Prior to the incident, the captain had two experiences with gear unsafe issues during maintenance check flights. The first officer discussed the missing "H" light with the captain, and they decided the gear was down and locked since three lights were illuminated. The first officer had been trained that three green lights override other indications. However, Great Lakes Aviation's Chief Pilot disagreed that this training was provided, stating the proper response would be a go-around and QRH use. The Director of Flight Standards noted that the crew should have executed a go-around but understood the confusion given the system schematic and the captain's previous gear problems. The QRH for manual extension states that failure of only one green annunciator does not indicate unsafe gear, but the manual extension system was disabled by the end cap failure. As a result, Great Lakes drafted changes to the QRH and revised training modules.