Houston, TX, USA
N213WQ
BOMBARDIER INC DHC-8-402
After take-off from the departure airport, the crew observed a master caution, an amber nose gear open advisory light, a landing gear inoperative caution light, and they noticed a different than normal airflow noise During the flight, the crew heard a "thump" and noted that the previously observed caution lights had extinguished indicating that the nose gear was retracted and the nose gear doors were closed. In accordance with abnormal procedures checklists, and guidance from the company, the crew elected to use the Alternate Landing Gear Extension checklist to prepare for landing at the destination After pulling the main gear release handle and the nose gear release handle the crew observed that the main landing gear indicated down and locked with green indicator lights, the nose landing gear did not indicate down and locked, and the red Nose Gear Unsafe light was illuminated. The crew landed the airplane with the main landing gear down and the nose landing gear retracted, and the airplane came to rest on the main gear and forward fuselage on the runway. Post-accident, the nose gear was successfully extended multiple times using the alternate extension handle and the landing gear was also extended multiple times under hydraulic power with no anomalies noted. Testing of landing gear system components did not reveal any failures that should have prevented the gear from extending via the alternate extension method. The pull force required to extend the nose gear alternate release handle to a position where the nose gear released from the up and locked position was measured at approximately 72 lbs. According to manufacturer's design requirements, the pull length on the alternate release handle should be approximately 11 inches with a force of 90 pounds. A post-accident review of the alternate gear extension procedures was conducted in a full flight simulator by the investigation group with the participation of the accident flight crew. The pull force required and the pull length required to extend the nose gear using the alternate extension handle was determined to be significantly lower in the flight simulator as compared to the aircraft. There was no guidance contained in the alternate landing gear extension procedure specifying required pull forces when using the alternate extension handle. Subsequent to the accident, the manufacturer added details to the alternate landing gear extension procedure in the Airplane Flight Manual regarding the maximum pull forces that a pilot may experience when the alternate extension handle is pulled.
HISTORY OF FLIGHT On April 7, 2012, about 1108 central daylight time, a Colgan Air Inc. Bombardier De Havilland DHC-8-402, N213WQ, operating as United Express flight 4915, landed with the nose gear retracted on runway 9 at George Bush Intercontinental / Houston Airport (IAH), Houston, Texas. There were no injuries to the 31 passengers and 4 crewmembers onboard and the airplane received substantial damage. The flight was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 as a regularly scheduled passenger flight from Adams Field Airport (LIT), Little Rock, Arkansas. The first officer was the pilot flying and the captain was the pilot monitoring for the flight. During climb out after departure from LIT the first officer and the captain noticed a different airflow noise than normal when the landing gear was selected up. They observed an amber nose gear door open advisory light, a master caution, and a landing gear inoperative caution light. The three green gear indication lights and three red gear indication lights were extinguished indicating the landing gear was retracted. The captain performed the Nose Gear Door Malfunctions check list contained in the Quick Reference Handbook and the crew maintained airspeed of at or below 185 knots for the remainder of the flight as stated in the checklist. During the flight to IAH, the crew heard a "thump" and observed the nose gear door amber status light and the LDG GEAR INOP caution light had extinguished. In accordance with the Nose Gear Door Malfunctions check list, and guidance received from company maintenance and system operations control via ACARS (Aircraft Communications Addressing and Reporting System), the crew elected to use the Alternate Landing Gear Extension checklist for landing at IAH. The crew exchanged roles as the captain became the pilot flying and the first officer assumed the role of pilot monitoring for the remainder of the flight. Approximately over the ROKIT intersection, about 50 miles from IAH, the first officer began to perform the Alternate Landing Gear Extension checklist. At 1533:34 the first officer pulled the main gear release handle and the nose gear release handle and observed that the main landing gear indicated down and locked with green indicator lights, the nose landing gear did not indicate down and locked, and the red Nose Gear Unsafe light was illuminated. The alternate gear indication lights in the floor near the nose gear release handle agreed with the primary gear indication lights on the flight deck panel. After the Alternate Gear Extension Procedure was completed, the crew could hear the nose gear door was "flapping loosely". The flight crew conducted a low approach and air traffic control tower personnel advised them that the nose gear doors appeared to be open but the nose gear did not appear to be down. At 1556:52 the captain briefed the cabin crew members and advised them that an evacuation, if necessary, would be conducted using the forward doors. The flight crew configured the airplane for landing at flaps 35 on runway 9 with the main landing gear down, and the nose landing gear retracted. At 1607:46, after passing through about 1,000 feet on approach, the first officer made a "brace" call over the passenger address system. The main gear touched down at 1608:50 and the captain held the nose off the runway until the airplane slowed to about 80 knots. Once the nose touched down, there were sparks and smoke resulting from the fuselage scraping the runway and the airplane came to a stop at about 1609. The captain ordered an evacuation and the pilots performed the On Ground Emergencies checklist. The passengers and crew evacuated through the forward cabin doors and were bussed to the terminal. INJURIES TO PERSONS There were no injuries to the 31 passengers or the 4 crewmembers on board. DAMAGE TO AIRPLANE The airplane was substantially damaged by deformation and abrasion due to runway contact. The lower forward fuselage was dragged along the runway resulting in structural damage to the fuselage skin, stringers, and frames. The skin on the lower fuselage was worn through to structure creating a large hole in the area between Fuselage Stations X-124 to X-69. The forward nose landing gear doors were torn away from the fuselage. The aft nose landing gear doors were in the closed position with portions of the exterior surfaces scraped and worn down to the honeycomb. PERSONNEL INFORMATION The flight crew consisted of two pilots and two flight attendants. The captain, age 34, was hired by Colgan Air, Inc. in February 2006 as a captain on the Beechcraft BE-1900. He transitioned to captain on the Saab SF-340 in 2007, and then to the DHC-8 in April, 2011. At the time of the accident, he was based in Houston, Texas. The captain reported approximately 6,500 hours total time, including about 5,000 hours as pilot-in-command and 396 hours in the DHC-8. There were no records or reports of any previous aviation incidents or accidents involving the captain and a search of the National Driver Register found no record of driver's license suspension or revocation. The captain held a valid Federal Aviation Administration (FAA) Airline Transport Pilot (ATP) certificate with type ratings for BE-1900, SF-340, and DHC-8 and a current FAA first-class medical certificate with a limitation that he must wear corrective lenses. The captain indicated he was wearing corrective lenses at the time of the accident. Training and proficiency checks were current and the company reported that the captain had no record of failures during company training events. The first officer, 24 years old, was hired by Colgan Air, Inc. in October 2010. He was based in Houston, Texas and commuted to work from Minneapolis, Minnesota. He reported approximately 2,100 hours total flight time and about 900 hours in the DHC-8; all of which was second-in-command time. The were no records or reports of any previous aviation incidents or accidents involving the first officer and a search of the National Driver Register found no record or driver's license suspensions or revocations. He held a valid FAA commercial pilot certificate with an instrument rating and a DHC-8, SIC privileges only, type rating, and an FAA first-class medical certificate. The first officer's training and proficiency checks were current and the company reported he had no failures recorded during company training events. The captain and first officer had not flown together previously. The accident occurred on the second leg on the first day of a four day trip. AIRCRAFT INFORMATION N213WQ, manufacturer serial number 4213, was a Bombardier De Havilland DHC-8-402 equipped with two Pratt and Whitney PW150A turbo-prop engines. The company reported that the airplane had approximately 7,936 hours total time on the airframe. Recorded data and airline records indicated no relevant maintenance issues with the airplane. At the time of the accident the estimated landing weight was 50,136 pounds. Landing Gear System The landing gear is electrically controlled, hydraulically operated and mechanically locked. The main landing gear (MLG) retracts aft into the nacelles and the nose landing gear (NLG) retracts forward into the nose section. The landing gear is operated by the No. 2 hydraulic system. It is controlled by the landing gear selector lever on the landing gear control panel in the flight deck. There is an alternate means of extension for the landing gear in the event that the primary system is not functioning. Advisory lights in the flight deck provide extension and retraction information to the flight crew. The alternate extension system can be used to extend the landing gear when the No. 2 hydraulic system is not serviceable. The system can also be used if the normal extension system fails to lock the landing gear in the down position. The alternate extension system is a self-resetting, cable actuated design. Access to the alternate extension system is through the flight compartment. The alternate extension system includes a bypass valve to isolate the landing gear hydraulics from the No. 2 hydraulic system. A manual hand pump hydraulic system is available to assist in locking the main landing gear into the down and locked position. The alternate extension mechanically releases the NLG forward doors, the MLG aft doors, and all landing gear uplocks are mechanically opened. The NLG free falls to the down and locked position, assisted by the airflow. The MLG freefalls and, if required, are pumped to the locked position by the alternate extension actuators. Landing Gear Alternate Extension To isolate the normal landing gear selector valve during flight, a landing gear inhibit switch is installed in the flight compartment ceiling. To use the alternate extension system, the landing gear inhibit switch must first be set from normal to inhibit. The landing gear alternate release handle, accessed via the landing gear alternate release door in the ceiling of the flight deck compartment, is pulled to open the MLG doors and release the MLG uplocks. Tension springs in the MLG door mechanism pull the doors open and the MLG freefalls into the down position. Springs installed on the MLG stabilizer brace move the lock links into the down and locked position. A hand pump located in the flight compartment floor can be used to fully extend the MLG if necessary. The landing gear alternate extension handle in the flight deck compartment floor is pulled to release the NLG. The first stage of the pull unlocks the NLG forward doors. Tension springs in the NLG door mechanism assist to pull the doors open. As the handle is pulled further, the NLG uplock is released. The NLG free falls to the fully extended position. Springs installed on the NLG drag strut move the lock links into the down and locked position. The Bombardier Design Philosophy and Description document stated that for the nose landing gear alternate extension system, the pull handle travel is approximately 11 inches with a force of 90 pounds maximum. Guidance to all operators of the DHC-8-400 from Bombardier indicated that flight crews must ensure the main and nose gear release handles are pulled with sufficient force (which may exceed 90 pounds) to release the doors and uplocks. The operator's Quick Reference Handbook utilized by flight crew members on the flight deck included a note which stated that the "Gear release handle loads may exceed those experienced during practice sessions". Landing Gear Advisory Lights Landing gear and gear door position is shown by nine advisory lights on the landing gear control panel, and an amber light in the selector lever. The L. DOOR, N. DOOR, or R. DOOR amber lights illuminate when the related hydraulic gear door is open. The LEFT, NOSE, RIGHT green lights are illuminated when the related gear is down and locked and the LEFT, NOSE, RIGHT red lights are illuminated when the related gear is not locked in the selected position. When the gear is up and locked all lights on the landing gear control panel go off. The amber light in the landing gear selector lever will be illuminated when the actual position of any gear is contradicting the position of the lever, concurrent with the individual red lights on the landing gear control panel. When the indication on the landing gear control panel is not available, an alternate downlock indication system is available on the landing gear alternate extension panel on the flight compartment floor. The system provides a green light indication for each landing gear when the landing gear is down and locked. METEOROLOGICAL INFORMATION The IAH surface observation at 1053 CDT reported wind from 120 degrees at 9 knots, visibility 10 miles, few clouds at 3,500 feet, scattered clouds at 25,000 feet, temperature 25 degrees Celsius, dew point temperature 17 degrees Celsius, and altimeter setting 30.12 inches of mercury. AERODROME INFORMATION The George Bush Intercontinental / Houston Airport (IAH) is located about 15 miles north of the city of Houston, Texas. The airport conducts operations using 10 runways for commercial and general aviation. Runway 9 is grooved concrete, 10,000 feet long, 150 feet wide with a touchdown zone elevation of 92 feet. The runway is served by a 4-light precision approach path indicator system (PAPI) with a 3 degree glide path on the right side of the runway, and a medium intensity approach light system with runway alignment indicator lights (MALSR). FLIGHT RECORDERS The cockpit voice recorder (CVR), a Honeywell 6022 SSCVR 120, serial number CVR120-10121, was removed from the airplane and downloaded at the NTSB Vehicle Recorder Laboratory. The CVR contained 2 hours, 4 minutes, 54 seconds of recording on five audio channels. The audio quality of each channel was characterized as good to excellent, and the recording included events from the entire flight beginning with ground operations prior to departure from LIT. Timing on the transcript was established by correlating the CVR events to common events on the flight data recorder (FDR). The FDR, a Honeywell SSFDR 980-4700-027, serial number SSFDR-13637, was removed from the airplane and sent to the NTSB Vehicle Recorders Division. The recorder was found to be in good condition, and contained approximately 27.2 hours of data. The data were extracted normally. Correlation of the FDR data to event local time, central daylight time, was established by using the recorded time Universal Coordinated Time (UTC), Minutes, hours, and seconds parameters and applying an additional -5 hours offset to change from UTC to local CDT. WRECKAGE AND IMPACT INFORMATION As a result of the damage to the lower forward fuselage, the aft nose gear doors had to be removed to allow inspection of the landing gear. The nose landing gear was found in the up and locked position with wheels straight. The lower portion of the gear box, outer cylinder, trunnion pins, and centering cam housing were scraped and worn down. The NLG door bell-crank was found in the door open position. The door rods were slightly bent and the rod end attachments to the doors were ripped off. The bell crank was able to contact the door closed sensor bracket when toggled. All other mechanical systems including the lock actuator, uplock mechanism, springs, retract actuator, NLG door actuator, mechanical sequence valve, and visible NLG alternate extension components were intact and secure. Initial inspection of the flight deck indicated that the landing gear selector lever was in the down position, the landing gear inhibit switch was in the inhibit position, and the alternate landing gear release door and landing gear alternate extension door were both open. MEDICAL AND PATHOLOGICAL INFORMATION On April 7, 2012, the captain and first officer complied with a company request to submit to drug and alcohol screening tests. Results of these tests were negative for alcohol and major drugs of abuse. TESTS AND RESEARCH The nose of the aircraft was jacked and the nose gear alternate extension handle was pulled to the fully extended position. The NLG released normally and extended to the down and locked position. The gear was then manually retracted to the up and locked position and a second alternate extension of the nose landing gear was performed. The gear again released normally and extended to the down and locked position. The pull force required to extend the nose gear alternate release handle to a position where the nose gear released from the up and locked position was measured at approximately 72 lbs. Due to the damage incurred during the incident landing, the nose door ground lock was installed and a new nose wheel centering sensor was wired to the gear assembly. The hydraulic system was then powered and the NLG was cycled through extend/retract sequence 5 times with no anomalies noted. The alternate gear extension method was attempted three more times while the system was powered with no anomalies noted. Various components of the nose landing gear system were removed for further examination
the nose landing gear alternate release handle was not pulled with sufficient enough force or distance to release the uplocks and allow extension of the nose landing gear. Contributing to the accident was the dissimilar pull force and pull length set on the flight simulator that was used for flight crew training of alternate landing gear extension procedures and the lack of information available to crew members advising of the dissimilar pull force.
Source: NTSB Aviation Accident Database
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