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three green gear indication lights and three red gear indication lights were extinguished indicating the landing gear was retracted.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 including acceptance test procedures (ATP), disassembly and inspection.
The mechanical sequence valve was tested and examined. The unit passed all portions of the ATP except for the manual operating force test. The unit initially exceeded the force requirements of this test. Disassembly revealed that the true position of the 0.437/0.438 inch diameter bore was out by as much as 0.015 inches and some anomalies were noted in this area.
The solenoid sequence valve which controls opening and closing of the nose landing gear doors passed all portions of the ATP except the drop-out voltage test at the port labeled "C1". The drop-out voltage recorded was 2.9 VDC. The ATP requires a drop-out voltage between 7.8 and 3.0 VDC. During disassembly some metallic like debris was discovered and small nicks were noted on a seal land on the sleeve.
The nose landing gear retraction actuator which extends and retracts the nose landing gear, and the nose landing gear lock actuator which assists with locking and unlocking the nose landing gear were functionally tested per modified component maintenance manual procedures and no abnormalities were noted. Disassembly and inspection of these components indicated no concerning irregularities.
The nose landing gear door actuator which operates the opening and closing of the nose landing gear doors completed all modified component maintenance manual tests successfully except for the "Low Pressure Leakage" test and the "Proof Pressure and Leakage" test. Disassembly and inspection of the nose landing gear door actuator identified metallic debris and signs of scoring on the internal surface of the cylinder assembly along the direction of piston rod travel. Inspection of the piston rod revealed damage and missing material on the seal lands.
The on-scene download of the Proximity Sensor Electronics Unit (PSEU) fault history indicated all current faults were consistent with, and expected, based on the aircraft configuration at time of testing. The fault history indicated the nose landing gear door closed sensor faulted both "Open" and "Short" on the incident flight, and "Open" on the previous flight. Following download of the fault history, the PSEU successfully completed all ATP except for a lower than expected inductance reading for the nose gear Lock 1 target in the NEAR condition.
The nose landing gear closed sensor provides a "doors closed" or a "doors not closed" signal for the forward nose landing gear doors. Post-accident examination and testing revealed the sensor was cracked and that it failed the inductance and shield continuity test portions of the ATP.
The two nose landing gear lock sensors, "NGLK1" and "NGLK2", that provide a nose landing gear locked signal to the PSEU when the nose gear is locked in either the up or down position were subjected to the insulation resistance, high potential, and return to service inductance test portions of the ATP while still connected to their wiring harness assemblies. All tests were passed except the "NGLK1" sensor failed the return to service inductance test.
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 flight crew stated that the pull force required for the landing gear alternate release handle in the flight simulator was much less than the pull force encountered in the airplane.
ORGANIZATIONAL AND MANAGEMENT INFORMATION
Information provided by the company indicated that Colgan Air, Inc. had a total of 1,335 employees including 543 pilots. The company had 56 airplanes including 28 Saab-340s and 28 Bombardier DHC-8-400s. The company had flight crew bases in Houston, TX, Newark, New Jersey, the Washington DC area, Memphis, Tennessee, Minneapolis, Minnesota, Atlanta, Georgia, and Detroit, Michigan.
Colgan Air, Inc. was acquired by parent company Pinnacle Airlines in 2007, which also owned Mesaba Airlines. Colgan Air, Inc. corporate offices were located in Memphis, Tennessee and they operated 276 flights daily under codeshare agreements as United Express and US Airways Express. Colgan Air, Inc. ceased operation on September 5, 2012.
ADDITIONAL INFORMATION
Interviews with company training personnel indicated that flight crews normally performed an alternate landing gear extension during training in the flight simulator. Instructors did not have an option to program the simulator to prevent the nose gear from extending during an alternate landing gear extension procedure.
Following the accident, Bombardier amended the Airplane Flight Manual to include a note in the alternate landing gear extension procedure which read "The nose gear release handle pull force will be significantly higher than experienced during practice alternate landing gear extensions. The required pull force, to release the nose gear uplock, can be as high as 41 kg (90 lb). It may require a repeated pull effort to achieve a nose landing gear down and locked indication."
Following the accident, Colgan Air issued a Fleet Memo for flight crew members to emphasize that gear release may require a pull force of up to 90 pounds and that flight crews should consider repeating the procedure if not initially successful. The company also drafted a revision to the Quick Reference Handbook that included clarifications of alternate landing gear extension procedures and required pull force for release of the landing gear using the Alternate Landing Gear Extension Procedure. The new procedures included the following note:
1. The nose gear release handle pull force will be significantly higher than experienced during alternate landing gear extensions in the simulator. 2. The required pull force, to release the nose gear uplock, will be as high as 90 pounds. 3. If nose landing gear down-and-locked indication is not achieved, PM should assume whatever position necessary; and repeat pull action with whatever force necessary to achieve a down-and-locked indication.