Thursday, July 13, 2017

North American TB-25N Mitchell, N25YR, registered to American Airpower Heritage Fly Museum and operated by Central Texas Wing of the Commemorative Air Force (CAF): Accident occurred October 29, 2016 near Dallas Executive Airport (KRBD), Texas

Aviation Accident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

NTSB Identification: CEN17LA033 
14 CFR Part 91: General Aviation
Accident occurred Saturday, October 29, 2016 in Dallas, TX
Probable Cause Approval Date: 09/06/2017
Aircraft: NORTH AMERICAN TB 25N, registration: N25YR
Injuries: 9 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The airline transport pilot reported that the twin-engine, historic airplane was flying about 155 mph and 1,000 ft above ground level. Upon entering the left downwind leg of the airport traffic pattern, the pilot extended the landing gear. While the gear was in transit, the crew felt a jolt, as if a bird had impacted the front of the airplane. The pilot made a normal landing, parked the airplane, and noted damage to the left horizontal stabilizer and elevator.

A crew from another airplane reported to the pilot that they observed an object depart the accident airplane during landing gear extension. A postaccident examination revealed that the left inboard landing gear door separated in flight and impacted the engine nacelle, left horizontal stabilizer, and elevator. The landing gear door was later found in a field about 1.5 miles from the airport. The gear door was equipped with two arresting cables that were intended to prevent the door from hyperextending. The arresting cables were not installed in the correct position, and the investigation could not determine how long the arresting cables had been incorrectly installed. The landing gear door connecting rod was bent and fractured into two pieces at the safety wire drill hole. The fractured connecting rod was consistent with an overstress failure in bending. If the arresting cables had been installed correctly, it is likely that the landing gear door would not have separated from the airplane when the connecting rod failed.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The overstress failure of the landing gear connecting rod and the improper installation of the arresting cables, which allowed the landing gear door to depart in flight and impact the airplane.

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Irving, Texas

Aviation Accident Factual Report - National Transportation Safety Board: https://app.ntsb.gov/pdf


Registered to American Airpower Heritage Fly Museum

Operated by the Central Texas Wing of the Commemorative Air Force (CAF) 

http://registry.faa.gov/N25YR




NTSB Identification: CEN17LA033
14 CFR Part 91: General Aviation
Accident occurred Saturday, October 29, 2016 in Dallas, TX
Aircraft: NORTH AMERICAN TB 25N, registration: N25YR
Injuries: 9 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

HISTORY OF FLIGHT

On October 29, 2016, about 1540 central daylight time, a North American TB-25N airplane, N25YR, was damaged when the left inboard landing gear door separated in flight. The airline transport rated pilot, airline transport rated co-pilot, and seven passengers were not injured. The airplane sustained substantial damage. The airplane was registered to American Airpower Heritage Fly Museum and operated by the Central Texas Wing of the Commemorative Air Force (CAF) under the provisions of 14 Code of Federal Regulations Part 91 as an airshow flight. The local flight departed from the Dallas Executive Airport (RBD), Dallas, Texas, about 1500 and landed at RBD about 1545. 

The pilot reported that the airplane was flying about 155 mph and 1,000 ft above ground level, when the airplane entered the traffic pattern. The landing gear was lowered on the downwind leg and when the gear was in transit the crew felt a jolt as if a bird had impacted the front of the airplane. The pilot noted that the main gear extended normally, but the nose gear was slow to indicate a down and locked position. He then felt a flight shudder from the airplane and a few seconds later the nose gear down indication was confirmed. He checked the flight controls for functionality with no abnormalities noted. He made a normal landing and parked the airplane. 

The crew from another airplane reported to the pilot that they observed an object depart the accident airplane as the landing gear was extended in the traffic pattern. Witnesses on the ground reported observing the same event. 

According to the responding Federal Aviation Administration (FAA) inspector, the left inboard landing gear door separated in flight and impacted the nacelle and then the left horizontal stabilizer and elevator. The airplane made an uneventful landing at RBD where damage was observed to the left horizontal stabilizer and elevator. The landing gear door was found in a field about 1.5 miles from RBD.

AIRCRAFT INFORMATION 

A review of the maintenance logbooks revealed that a Phase B inspection, as a part of the continuous inspection program, was completed on February 12, 2016. There were no logbooks entries pertaining to the landing gear door and the operator stated they did not have any discrepancies with the associated components. 

According to the airplane's operating manual, the maximum gear extended speed is 170 mph. 

METEOROLOGICAL INFORMATION 

The automated weather station located at RBD recorded wind from 170 degrees at 7 knots, gusting to 16 knots, 10 miles visibility, clear sky, temperature 82 degrees F, dew point 57 degrees F, and altimeter setting 30.05 inches of mercury. 

TESTS AND RESEARCH

The landing gear door connecting rod assembly was found fractured into two pieces and was sent to the NTSB Materials Laboratory, Washington, DC, for examination. The examination revealed that one end of the connecting rod was outfitted with a spherical bearing rod end and the other end was outfitted with a clevis rod end. The clevis end was bent along the shank. The bend axis was perpendicular to the clevis hinge. The spherical bearing rod end was fractured in the threaded portion of the shank in the same plane as a drill hole for safety wire. There were no features indicative of a preexisting crack. Microscopic examination of the fracture surface revealed tear lines radiating away from the safety wire drill hole on the outer bend side of the fracture. The features observed on the connecting rod assembly were consistent with an overstress failure in bending.

ADDITIONAL INFORMATION

The CAF Director of Maintenance reported that the landing gear door connecting rod was bent and fractured into two pieces at the safety wire hole. The gear door is equipped with two arresting cables that are intended to prevent the door from hyperextending. He also reported that the arresting cables were not installed in the correct position. The investigation could not determine how long the arresting cables has been incorrectly installed. 


The CAF Director of Maintenance issued an internal safety bulletin to warn the other B-25 crew of the safety issue. The bulletin noted that the inner gear door attachment rod bolt failed upon gear extension which allowed the door to fly open breaking both hinges and grounding straps. The door then struck the left horizontal stabilizer on the leading edge then passed under the horizontal and struck the elevator where it tore the fabric and bent one rib. The bulletin recommended to remove the safety wire and inner landing gear door bolts and inspect the mechanical gear door linkage for signs of stress. The door connecting rods must both push the doors open and then pull them closed. Once closed, the doors are held in position in tension by these connecting rods. Carefully inspect the shorter inner adjustment bolt for any signs of bending especially near the top attachment point.

NTSB Identification: CEN17LA033
14 CFR Part 91: General Aviation
Accident occurred Saturday, October 29, 2016 in Dallas, TX
Aircraft: NORTH AMERICAN TB 25N, registration: N25YR
Injuries: 9 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On October 29, 2016, about 1730 central daylight time, a North American TB-25N airplane, was damaged when the left inboard landing gear door separated in flight. The airline transport rated pilot, airline transport rated co-pilot, and seven passengers were not injured. The airplane sustained substantial damage. The airplane was registered to and operated by American Airpower Heritage Fly Museum, Dallas, Texas, under the provisions of 14 Code of Federal Regulations Part 91 as an airshow flight. The local flight departed from the Dallas Executive Airport (RBD), Dallas, Texas, about 1500 and landed at RBD about 1545. 

According to the responding Federal Aviation Administration (FAA) inspector, the left inboard landing gear door separated from its attachment point while in flight and impacted the nacelle and then the left horizontal stabilizer and elevator. The landing gear door was found in a field about 1.5 miles from RBD. 

The airplane has been retained for further examination.

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