Avions Mudry Cie CAP 231 accident near Lebanon, Pennsylvania, May 27, 2017
On May 27, 2017 at about 5:30 pm local time, a 1990 Avions Mudry Cie CAP 231, registered N231X, was substantially damaged in an accident during maneuvering (aerobatics) near Lebanon, Pennsylvania (Keller Brothers Airport). It was a personal flight under general aviation rules (Part 91). No one was hurt; 1 person was on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The partial separation of one counterweight and the subsequent seizure of the engine due to mechanical interference. Contributing to the partial separation of the counterweight was the overstress fracture of a retaining ring and the fatigue fracture of the counterweight washer for reasons that could not be determined based on the available evidence.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- May 27, 2017 · about 5:30 pm local time
- Place
- Lebanon, Pennsylvania · Keller Brothers Airport · map
- Type
- Accident
- Injuries
- No one was hurt; 1 person was on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Avions Mudry Cie CAP 231 UNDESIGNAT, built 1990
- Registration
- N231X · no longer on the register · serial 12
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The private pilot reported that he was practicing aerobatics near the departure airport and that the airplane was in a 45° nose-up maneuver when he heard a "loud knock" from the engine, followed by a significant "shake." He leveled the airplane, reduced the manifold pressure, and then turned the airplane back toward the airport. Subsequently, the engine rattled and began to shake more, followed by a total loss of power. The pilot's attempts to restart the engine were unsuccessful. He planned a high base leg and sideslip onto the final approach leg of the airport traffic pattern to ensure the airplane would reach the runway. During the landing flare, the airplane floated, touched down beyond the midpoint of the grass runway, and bounced. The pilot applied hard braking, but the airplane rolled off the end of the runway, down an embankment, and nosed over. Postaccident examination of the engine revealed that it was seized and that one counterweight, which was normally secured to the crankshaft at two places, was separated at one location. The retaining ring for one side of one counterweight, which was properly installed, fractured due to overstress, and its associated washer fractured due to reverse bending fatigue. The fracture of these components allowed the roller to separate and jam between the crankcase and crankshaft, which resulted in mechanical interference. The roller's contact with the counterweight bushings and/or counterweight washers could have been caused by a several things; however, because the fatigue crack initiation sites were destroyed by postfracture damage, the root cause for the overstress fracture of the retaining ring and fatigue fracture of the washer associated with the counterweight could not be determined.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Loss of engine power (total) during maneuvering (aerobatics) defining event
- Attempted remediation/recovery during maneuvering (aerobatics)
- Miscellaneous/other during landing (flare/touchdown)
- Runway excursion during landing (landing roll)
- Nose over/nose down during landing (landing roll)
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine (reciprocating) › Recip engine power section › Malfunction
- cause Aircraft › Aircraft power plant › Engine (reciprocating) › Recip engine power section › Failure
- factor Aircraft › Aircraft power plant › Engine (reciprocating) › Recip engine power section › Fatigue/wear/corrosion
- factor Not determined › Not determined › (general) › (general) › Unknown/Not determined
Pilot
- Certificate: commercial pilot, private
- Ratings: multi-engine land; single-engine land; instrument: airplane
- Flight time: 2,308 hours in all; 57 in this make and model; 3 in the last 90 days; 0.2 in the last 30 days; 2,232 as pilot in command
- Last flight review: July 11, 2015
- Medical certificate: Class 3 (with waivers/limitations)
- Seat: sngl
- Injury: no injuries
The aircraft
- Airframe total time: 1,081 hours
- Last inspection: condition inspection, March 15, 2017; 3 hours since
- Maximum gross weight: 1,808 lb
- Seats: 1
- Landing gear: fixed
- Engine: Lycoming AEIO-540-L1B5 (piston); 0 hours total
The flight
- Departed from: 08N Lebanon PA at 5:20 pm
- Destination: 08N Lebanon PA
- Flight plan: none
- Runway 25, 2,692 ft by 120 ft
Weather at the time
- Light: daylight
- Wind: from 230° at 5 knots
- Visibility: 10 statute miles
- Sky: overcast at 4,700 ft
- Temperature: 70°F (21°C), dew point 57°F (14°C)
- Altimeter: 29.90 inHg
- Observation at 5:53 pm from LNS, 10 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Other NTSB records under N231X the same tail number, which may have belonged to a different aircraft at the time
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.