NTSB Factual Report

HISTORY OF FLIGHT

On August 23, 2003, at 1919 mountain daylight time, a Beech 1900D, N192GL, owned by Great Lakes Aviation, Limited, and operating as Great Lakes Airlines Flight 7079, sustained minor damage when the cabin air stair door opened during climb, approximately 15 nautical miles east-southeast of Denver, Colorado. Cabin pressure was subsequently lost. The crew declared an emergency and made an uneventful landing at Denver International Airport (DEN), Denver, Colorado. The airline transport certificated captain, first officer, and 14 passengers were not injured. Visual meteorological conditions prevailed at the time of the incident. The scheduled domestic passenger flight was being conducted on an instrument flight rules flight plan under the provisions of Title 14 CFR Part 121. The flight from DEN to Santa Fe, New Mexico, originated at approximately 1910.

The first officer reported that as part of the first flight of the day, he performed the cabin/cargo door checks. He said, "All checks of the cabin and cargo door circuitry appeared normal." The first officer said that the air stair operated normally during the three previous flights that day. He reported that on the incident flight, he "did not note any abnormalities as far as the operation/locking of the forward air stair door." He said that the cabin door annunciator light went out as normal after closing and locking the cabin door. He and the captain verified that the doors were closed and the annunciator lights were out. After completing the taxi checklists and before takeoff checklists, they were instructed to taxi to runway 17L. The first officer said that at no time during the taxi did any warning lights illuminate.

The captain reported that approximately 5 minutes into the flight and passing 8,000 feet mean sea level (msl), the cabin door warning light illuminated. The captain said they ran the checklist, which directed the passengers to ensure their seat belts were fastened. The captain stated he directed the first officer to tell Denver Approach Control that they were returning to the airport. The captain said they did not declare an emergency at that time. The captain reported that approximately 2 minutes after the cabin door warning light illuminated, he initiated a 20 to 25 degree bank left turn to take them back to the airport. During the turn, the captain said he heard a pop and the cabin door came open. They declared an emergency at that time. The captain said they landed with the cabin door open.

AIRCRAFT INFORMATION

The airplane was a Beech 1900D passenger liner, serial number UE-192, owned and operated by Great Lakes Aviation, Limited, and used for carrying passengers on scheduled, domestic flights. The airplane was being maintained under a continuous maintenance program. The most recent inspection of the airplane was done on August 19, 2003. At that time, the airplane had 17,471.9 total hours. At the time of the incident, the airplane had 17, 493.7 total hours.

PERSONNEL INFORMATION

The captain held an airline transport pilot certificate with single and multiengine land, and instrument airplane ratings. The captain also held a flight instructor certificate with a single engine land rating.

The captain successfully completed a company flight proficiency check on July 13, 2003. The captain reported having 2,850.3 total flying hour; 2,477.3 hours were in Beech 1900s.

The captain held a first class medical certificate dated May 7, 2003. The certificate showed no limitations.

The first officer held a commercial pilot certificate with single and multiengine land, and instrument airplane ratings. The first officer also held a flight instructor certificate with single and multiengine land and instrument airplane ratings.

The first officer successfully completed a company flight proficiency check on December 1, 2002. The first officer reported having 1,541 total flying hours with 654 hours in Beech 1900s.

The first officer held a first class medical certificate dated August 20, 2003. The certificate showed the following limitation: "Holder shall wear lenses that correct for distance vision and possess glasses that correct for near vision.

WRECKAGE AND IMPACT INFORMATION

The airplane was examined at Denver, Colorado, at 2200. The airplane's cabin air stair door was hyper-extended in the open position. The door's aft upper support cable was snapped approximately 51 inches outboard of the cable attachment at the top aft corner of the door. The cable was unraveled at the fracture showing evidence of overload. The cable sheathing was pulled apart. The "snubber" arm at the front of the door was bent downward 90-degrees. The snubber cable was broken out at the bolt attachment at the end of the arm. The top 6 inches of the cable were missing. The remaining cable was fractured, kinked, and unraveled. The door hydraulic cylinder arm was in the "door closed" position. The door hinge, located along the bottom of the door, was bent outward and aft. The air stair door was bent outward in two places; the first, approximately 21 inches outboard of the hinge, and the second, approximately 46 inches outboard of the hinge. The top two steps on the air stair were cracked at the bases. The inside door handle was observed in the unlocked and open position. The door handle was bent laterally forward approximately 10 degrees. The door's eight cam locks showed no damage. The door frame aft inside bulkhead was cracked at the upper outside corner.

The left propeller showed damage to 2 of its 4 blades. One blade had a 3/4-inch nick in the blade tip. The second blade showed a 1/8-inch nick in the leading edge near mid-span.

Flight control continuity was confirmed. A field examination of the door locking mechanism and cabin door warning light showed no anomalies. The cabin door, flight data recorder, and cockpit voice recorder were retained for further examination.

TESTS AND RESEARCH

The cabin air stair door was examined at Great Lakes Aviation, Limited, Cheyenne, Wyoming on August 26, 2003. Company maintenance records showed the door had 2,240.9 hours total time and 2,853 cycles. The manufacturer directs the door's overhaul at 12,000 hours or 16,000 cycles. The door handle and locking mechanism were tested. When the handle was moved to the locked position and pushed to the point where no further movement was noted, the 8 cam locks rotated approximately 180-degrees and the pressure lock plunger engaged the latch plate, locking the handle in place, as specified by the manufacturer. The latch cables and turnbuckles moved freely and showed proper tension. An examination of the door sensor to the forward cabin door warning light on the annunciator panel showed that the door handle could be placed in a position where the door's pressure lock plunger was just engaging the latch plate, but had not dropped into the "keyhole," and the warning light would go out. When moving the handle through the closed position so that the handle could no longer move forward, the pressure lock plunger would fully engage in its "seated position" and the warning light would go out. Backward pressure was then applied to the handle. With the pressure lock plunger engaged, the handle could not be moved from the closed position until the door latch-release button was depressed. The manufacturer's specifications for maintenance of the air stair door and pressure lock switch states, "The pressure lock plunger rides in the keyway at a point 0.04 inch or less from where the plunger drops into the keyhole ... Adjust the pressure lock switch so that it closes, illuminating the FWD CABIN DOOR light, with the plunger pulled up between .03 and .09 inch from its fully seated position." This test was performed on several other Great Lakes Aviation, Limited, Beech 1900 airplanes. In those tests, the same anomaly could not be duplicated.

The airplane's cockpit voice recorder (CVR) was examined at the National Transportation Safety Board's CVR Laboratory, Washington, DC, on August 27, 2003. The recording started after the airplane left the gate. The airplane was ground delayed for approximately 19 minutes. The airplane was airborne for approximately 10 minutes. During the flight, all communications were normal up to the point where the crew noted the cabin door warning light was on. According to the recording, 1 minute 32 seconds into the flight, the crew observed the Cabin Door Annunciator warning light illuminate. The crew started the appropriate checklist. According to the recording, 1 minute and 41 seconds later, a loud air noise was heard. The crew then declared an emergency and asked for an immediate return to land at Denver. The crew landed the airplane on runway 26, 10 minutes and 20 seconds after takeoff. The recording ended 2 minutes and 25 seconds later as the crew cleared the runway and shut down the engines.

The airplane's digital flight data recorder (DFDR) was examined at the National Transportation Safety Board's Vehicle Performance Laboratory, Washington, DC, on August 28, 2003. The DFDR data showed the airplane takeoff to the south, and begin a climb from approximately 5,200 feet msl. The data showed the airplane reach a maximum altitude of approximately 9,600 feet msl. approximately 3 minutes and 30 seconds into the flight. The data showed the airplane initiate a left turn and begin a gradual descent, rolling out on an approximate heading of 360 degrees. About 7 minutes and 10 seconds into the flight, the data showed the airplane making a gradual turn to a heading of approximately 260 degrees The airplane remained on this heading through landing. The data showed the airplane reach a maximum speed of approximately 200 knots during the flight. The data showed the flight duration as approximately 10 minutes.

ADDITIONAL INFORMATION

Parties to the investigation were the Federal Aviation Administration, Denver, Colorado, the Raytheon Aircraft Company, and Great Lakes Aviation, Limited.

The cabin air stair door and the flight recorders were released to Great Lakes Aviation, Limited, on October 14, 2003.

NTSB Probable Cause

the first officer's improper preflight preparation in failing to ensure the cabin airstair door was fully locked and secure. Factors relating to the incident were the cabin airstair door handle not being fully secure and the forward cabin door warning light not illuminating until the airplane was in flight.