History of Flight
On April 7, 2012, at about 1108 central daylight time, a Colgan Air Inc. Bombardier De Havilland DHC-8-402, registration N213WQ, operating as United Express flight 4915, landed with the nose gear retracted on runway 9 at George Bush Intercontinental / Houston Airport (IAH) in Houston, Texas. The flight was a regularly scheduled passenger service under 14 Code of Federal Regulations Part 121 from Adams Field Airport (LIT) in Little Rock, Arkansas. There were no injuries to the 31 passengers and 4 crewmembers on board; the airplane received substantial damage.
The first officer was the pilot flying and the captain was the pilot monitoring during departure from LIT. During climb after gear retraction, both pilots noted an unusual airflow noise. An amber nose gear door open advisory light, a master caution, and a landing gear inoperative caution light appeared. The three green and three red gear indication lights were extinguished, indicating the gear was retracted. The captain executed the Nose Gear Door Malfunctions checklist from the Quick Reference Handbook. The crew maintained airspeed at or below 185 knots for the remainder of the flight as per the checklist.
During the flight to IAH, the crew heard a "thump" and observed that the nose gear door amber status light and the LDG GEAR INOP caution light had extinguished. Following the checklist and guidance from company maintenance and system operations control via ACARS, the crew elected to use the Alternate Landing Gear Extension checklist for landing at IAH.
The captain became the pilot flying, and the first officer assumed monitoring duties. About 50 miles from IAH, over the ROKIT intersection, the first officer began the Alternate Landing Gear Extension procedure. At 1533:34, the first officer pulled the main gear release handle and the nose gear release handle. The main gear indicated down and locked with green lights; the nose gear did not indicate down and locked, and the red Nose Gear Unsafe light illuminated. The alternate gear indication lights on the floor agreed with the primary panel.
After the procedure, the crew heard the nose gear door flapping. A low approach was conducted, and air traffic control tower personnel reported that the nose gear doors appeared open but the nose gear did not appear down. At 1556:52, the captain briefed the cabin crew on evacuation procedures using forward doors if needed. The aircraft was configured for landing at flaps 35 on runway 9 with main gear down and nose gear retracted.
At 1607:46, after passing 1,000 feet on approach, the first officer made a "brace" call over the PA system. The main gear touched down at 1608:50; the captain held the nose off the runway until the airplane slowed to about 80 knots. Upon nose touchdown, sparks and smoke occurred from fuselage scraping. The airplane stopped at about 1609. The captain ordered an evacuation; passengers and crew evacuated through forward cabin doors and were bussed to the terminal.
Injuries to Persons
There were no injuries to the 31 passengers or the 4 crewmembers.
Damage to Airplane
The airplane sustained substantial damage from deformation and abrasion due to runway contact. The lower forward fuselage was dragged along the runway, resulting in structural damage to skin, stringers, and frames. Skin on the lower fuselage was worn through, creating a large hole between fuselage stations X-124 to X-69. The forward nose gear doors were torn away; the aft nose gear doors were closed with scraped exterior surfaces worn down to honeycomb.
Personnel Information
The flight crew consisted of two pilots and two flight attendants. The captain, age 34, was hired by Colgan Air in February 2006. He held an ATP certificate with type ratings for BE-1900, SF-340, and DHC-8, and a first-class medical certificate with corrective lenses requirement. He reported about 6,500 total hours, including 5,000 as pilot-in-command and 396 hours in the DHC-8. The first officer, age 24, was hired in October 2010. He held a commercial pilot certificate with instrument rating and DHC-8 SIC type rating, and a first-class medical certificate. He reported about 2,100 total hours and 900 hours in the DHC-8. Both had current training and proficiency checks, and no previous incidents or accidents. The captain and first officer had not flown together previously; the accident occurred on the second leg of a four-day trip.
Aircraft Information
N213WQ (serial number 4213) was a Bombardier De Havilland DHC-8-402 equipped with two Pratt and Whitney PW150A turboprop engines. The airframe had about 7,936 total hours. Recorded data and airline records indicated no relevant maintenance issues. The estimated landing weight was 50,136 pounds. The landing gear system is electrically controlled, hydraulically operated, and mechanically locked. The alternate extension system is cable-actuated, with a manual hand pump for main gear locking. The alternate extension mechanically releases door uplocks; the nose gear freefalls assisted by airflow.
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°C, dew point 17°C, and altimeter 30.12 inches of mercury.
Aerodrome Information
George Bush Intercontinental Airport (IAH) is about 15 miles north of Houston. Runway 9 is grooved concrete, 10,000 feet long by 150 feet wide, with a touchdown zone elevation of 92 feet. It has a 4-light PAPI with 3-degree glide path and MALSR.
Flight Recorders
The CVR and FDR were recovered and read out normally. The CVR contained 2 hours 4 minutes 54 seconds of good audio; the FDR contained about 27.2 hours of data. Timing was correlated between recorders.
Wreckage and Impact Information
Post-accident inspection found the nose landing gear in the up and locked position with wheels straight. The lower gear box, outer cylinder, trunnion pins, and centering cam housing were scraped. The NLG door bell-crank was in the door open position; door rods were slightly bent and rod end attachments ripped off. The flight deck showed the gear selector lever down, inhibit switch in inhibit, and alternate release doors open.
Medical and Pathological Information
Both pilots submitted to drug and alcohol screening; results were negative for alcohol and major drugs of abuse.
Tests and Research
The nose gear was jacked and alternate extension performed twice; the gear released normally and extended to down and locked. Pull force measured about 72 pounds. The NLG was cycled hydraulically five times with no anomalies. The mechanical sequence valve failed the manual operating force test due to bore misalignment. The solenoid sequence valve failed drop-out voltage test (2.9 VDC vs. 3.0 minimum) and had metallic debris. The nose gear door actuator failed low pressure leakage tests and had internal scoring and debris. The PSEU fault history showed nose gear door closed sensor faults on the incident and previous flight. The nose gear door closed sensor was cracked and failed inductance tests. One of two nose gear lock sensors (NGLK1) failed return-to-service inductance test. The flight crew stated in a simulator review that the pull force required for the alternate release handle was much less than in the airplane.
Organizational and Management Information
Colgan Air had 1,335 employees including 543 pilots, and operated 56 airplanes (28 Saab-340s and 28 DHC-8-400s). The company was acquired by Pinnacle Airlines in 2007 and ceased operations on September 5, 2012.
Additional Information
Company training personnel reported that flight crews normally practiced alternate gear extension in a simulator that could not simulate a nose gear extension failure. After the accident, Bombardier amended the Airplane Flight Manual to note that the nose gear release handle pull force can be as high as 90 pounds and may require repeated pulls. Colgan Air issued a fleet memo and drafted QRH revisions emphasizing the required pull force and the possibility of repeating the procedure.