A Cessna 560 Citation Encore airplane, N654CE, was substantially damaged when two engine cowlings departed the airplane inflight over Benbrook, Texas. The pilot and the one passenger were not injured.
The airplane was climbing through flight level (FL) 225 for FL 380, when the pilot heard a “loud crashing noise” followed by a “turbulent air sound” he described as similar to flying with the main landing gear extended. At time of the initial noise, the pilot reported the airplane was on a heading of 255, the airspeed was about 265 to 270 kts, and the autopilot system was engaged. The autopilot system was set to lateral navigation and the vertical speed was set for 1,500 ft per minute for climbing.
The pilot reacted to the initial noise by disconnecting the autopilot system, announcing the issue to air traffic control (ATC), slowing down the airplane to 170 kts, and descending to 11,000 ft above mean sea level. There were no master caution or warning lights illuminated on the cockpit annunciation panel. The pilot initially thought the airplane had a main landing gear malfunction based of the sound of the airflow around the cabin. The pilot slowed the airplane further, cycled the main landing gear, cycled the flaps, and moved the flight controls. He reported everything checked out normal except the “turbulent air sound” which was exacerbated with rudder movement. The pilot decided the main landing gear was functioning normally and there was a problem with the empennage.
The pilot located the closest airport with a paved runway greater than a 5,000 ft length, contacted ATC, and proceeded to land at the Mineral Wells Airport (MWL), Texas. The pilot executed an uneventful landing at 15:45 and shutdown the airplane without further incident.
A post landing inspection revealed the top and bottom cowling for the number 2 (right) engine were missing.
A portion of the separated cowlings was found wrapped around the inboard section of the right horizontal stabilizer. A portion of the separated cowlings impacted the area between the leading edge of the vertical stabilizer and the top of the fuselage, resulting in substantial damage. The remaining pieces of the separated cowlings have not been recovered.
On-scene examination revealed that receptacle 29, at the forward inboard side of the lower cowl door, was missing its stud, snap ring, and grommet and that receptacles 26 and 28 were missing their grommets and snap rings but had retained their studs.
The most likely cause of the cowl door departure is that either the stud at receptacle 29 was left unlocked when the cowl door was attached, or an oversized stud was used at receptacle 29 that was able to rotate from the locked to unlocked position. Without the stud to examine and additional on-wing testing, it cannot be determined whether the stud at that location was a longer grip-length stud or if spontaneous unlocking of a longer grip-length stud is an actual possibility.
The reason for the separation of the cowlings could not be determined because the stud in question was not recovered.
Probable Cause: The in-flight separation of the upper and lower right engine cowlings for reasons that could not be determined based on available evidence.
Distance from Dallas-Love Field, TX to Midland International Air and Space Port, TX as the crow flies is 509 km (318 miles).
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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