- Location: Clearwater, Florida
- Accident Number: ERA24FA104
- Date & Time: February 1, 2024, 19:07 Local
- Registration: N6659L
Aircraft: Beech V35
- Aircraft Damage: Destroyed
- Defining Event: Fire/smoke (non-impact)
- Injuries: 3 Fatal, 1 Minor
- Flight Conducted Under: Part 91: General aviation - Personal
https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/193737/pdf
https://data.ntsb.gov/Docket?ProjectID=193737
On February 1, 2024, about 1907 eastern standard time, a Beech V35B airplane, N6659L, was destroyed when it impacted two residences and the ground near Clearwater, Florida. The commercial pilot and two occupants of one residence were fatally injured, and one occupant of the other residence sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
The pilot proceeded toward the destination airport, cancelled his instrument flight rules (IFR) clearance when about 5 nautical miles (nm) from the airport, then proceeded under visual flight rules (VFR) in night visual weather conditions. The airport, with which the pilot was unfamiliar, was non-towered, located in a densely populated area, and not equipped with a rotating beacon. After establishing contact on the airport’s common traffic advisory frequency (CTAF), the pilot announced that he was unable to locate the airport and asked repeatedly for the pilot-controlled runway lights to be turned on.
According to witnesses who were in the airport’s fixed based operator (FBO) facility and heard the CTAF communications, at the time of the pilot’s first request, the runway lights were already on medium intensity from an airplane that had just landed. One of the witnesses responded to the pilot’s request by keying the radio microphone seven times to turn the lights up to high intensity. The witnesses and pilots in a nearby airplane reported that they subsequently heard the pilot announce that he had a fire. One witness at the FBO asked the pilot to repeat what he said, but the pilot did not.
ADS-B data showed that the flight had approached the airport from the southeast headed northwest. Once it reached the airport, it proceeded northwest, parallel to and about 0.5 nm west of the runway, before continuing northwest and past the airport. It subsequently turned left (to the west, away from the airport), completed a 180° turn, then again passed the airport before continuing south.
About 2 minutes before the accident, the flight was flying about 900 ft pressure altitude, and the pilot set the transponder to emergency code 7700. The flight proceeded briefly east, then southeast. About 1 minute before the accident, the pilot reestablished contact with the air traffic controller at the facility with which he had previously canceled his IFR clearance. The pilot told the controller that he was proceeding to a different airport because he was unable to visually identify his original destination airport.
The controller advised the pilot that the flight was 1 mile south of his original destination airport then asked the pilot if he could turn to a heading 180° and maintain the present altitude. The pilot advised the controller, “I’m losing engine.” According to a sound spectrum study, at the time of this communication, the airplane’s engine was operating at 2,500 rpm. The controller asked the pilot if he could see another airport that was 3 miles ahead of his position (and closer than the alternative airport that the pilot mentioned), but the pilot did not respond. The flight continued southeast, then turned left and descended steeply until impact.
According to a review of the available data, during the airplane’s final 20-second descent, it attained a maximum descent rate of 5,836 ft per minute (fpm) and the groundspeed increased. Per the sound spectrum study, the engine rpm decreased to about 2,053 then was estimated to about 1,907 immediately before impact. Witnesses on the ground who saw the airplane’s descent reported seeing fire on the forward portion of the airplane. Although the engine rpm decreased immediately before impact, it could not be determined what the pilot meant when he advised the controller that he was losing the engine because, at that time, it was operating at 2,500 rpm, which was slightly below the maximum continuous takeoff propeller rpm.
Postaccident examination of the flight controls and engine drivetrain, ignition, air induction, exhaust, and lubrication systems revealed no evidence of preimpact failure or malfunction. The outlet fitting of the metering valve was impact-fractured, and the b-nut of the flexible fuel hose attached to this outlet fitting was not fully tight. The throttle body and metering valve and corresponding area of the engine oil sump exhibited clean burn areas without soot deposits, though after coming to rest those areas were shielded by dirt and the upwardly crushed engine cowlings.
No discrepancy with the threads of the flexible fuel hose or of the fractured outlet fitting at the metering valve was identified, and it was possible to successfully torque the b-nut to about the minimum specified value. Further, several other fuel fittings in the engine compartment were also impact-fractured (similar to the fractured outlet fitting), but their respective hoses’ b-nuts remained tightly secured.
The engine was installed about 7.5 years before the accident, and there was no record of any maintenance done to the area of the loose b-nut since. The engine had accumulated 583 operating hours since installation, so it is unlikely that the hose was not tightly secured at that time. It is also unlikely that it was loosened by impact or the effects of the postcrash fire. It is more likely that, at some point after engine installation, undocumented maintenance occurred to the fuel hose from the metering valve to the manifold valve, and unknown maintenance personnel failed to adequately torque the fuel hose b-nut at the metering valve outlet fitting.
Based on the severity of the observed thermal damage in the area of the throttle body and metering valve, the most likely fire scenario for the accident airplane was an in-flight fire occurring due to ignition of fuel leaking from the slightly loose fuel hose at the outlet of the fuel metering valve.
The steep descent immediately before impact was the pilot’s likely response to the in-flight engine compartment fire and his initiation of an emergency descent. Though the position of the fuel selector valve was found between the left and right tank positions, and the position at impact could not be determined from the available evidence, the engine rpm about 43 seconds before impact was 2,500. Although the engine rpm had decreased immediately before impact, it is likely that the pilot did not promptly turn off the fuel selector in accordance with the “Engine Fire in Flight” checklist after recognizing and reporting a fire on the destination airport’s CTAF. Thus, had the pilot promptly secured the fuel selector valve and in conjunction with the steep descent, it is possible that the extent of the in-flight fire could have been mitigated. Further, had the pilot been able to visually locate the destination airport, it is likely that the he could have landed the airplane earlier in the accident sequence.
The pilot had negative results for carboxyhemoglobin, and no pre-existing issue was found at autopsy. Thus, it is unlikely that any medical issue resulted in the pilot’s failure to arrest the airplane’s steep rate of descent before impact with the residences.
- Probable Cause: An in-flight engine compartment fire due to a partially loose flexible fuel hose b-nut at the fuel metering unit. Contributing to the severity of the accident was the pilot’s inability to visually identify the destination airport at night, which prolonged the in-flight emergency.
