History of Flight
On July 10, 2021, at about 1254 mountain standard time, a Beechcraft C-90 turboprop airplane, registration N3688P, was destroyed in an accident near Wikieup, Arizona. The pilot and an Air Tactical Group supervisor were fatally injured. The airplane was operated as a public-use firefighting aircraft in support of the Bureau of Land Management, conducting aerial reconnaissance and supervision.
The airplane had been on station for about 45 minutes over the Cedar Basin fire area. ADS-B data showed the airplane completed multiple orbits over the fire at about 2,500 ft above ground level (agl). The last data point indicated an airspeed of 151 knots, altitude about 2,300 ft agl, and in a descent, about 805 ft east southeast of the accident site. No distress call was overheard on the radio.
A witness observed the airplane in a steep dive toward the ground. It impacted the side of a ridgeline in mountainous desert terrain. The main wreckage was mostly consumed by a post-crash fire. Debris was scattered over several acres. Another witness saw the left wing falling to the ground after impact; the left wing had separated outboard of the nacelle and was located about 0.79 miles northeast of the main wreckage, without thermal damage.
Personnel Information
The pilot held an airline transport pilot certificate with airplane single- and multi-engine land ratings, flight instructor and ground instructor certificates, and instrument ratings. He was issued a second-class medical certificate on May 28, 2021. At that examination, he reported 10,000 total flight hours, with 150 in the last six months.
Aircraft Information
The airplane was a Beechcraft King Air C90 manufactured in 1980, configured for wildland fire aerial supervision under contract. The aircraft status sheet from July 9, 2021, showed 17,262.6 hours total time and 15,475 cycles.
The airplane began flying under contract to the United States Forest Service (USFS) in April 2007 and was used solely in the aerial supervision role during USFS contracts. Up through 2016, it was also used under the operator's Part 135 operation; after that, only for USFS contract, flight training, or check rides. Annual USFS mission usage was fewer than 365 hours, sometimes under 100.
The aerial supervision mission involved cruise flight from base to target area, descent to altitudes between 1,000 and 3,500 ft agl, circling in a right-hand orbit for about 3–4 hours, and returning. Crew included a pilot and one or two USFS Air Tactical Group Supervisors. Speeds were typically 120 to 150 kts.
Maintenance and Repair
The airplane's operator, Falcon Executive Aviation, Inc. (FEA), provided flight logs from May 26 to July 9, 2021. The airplane accrued 42.8 hours and 17 cycles under USFS contract, plus 5 hours and 9 cycles for maintenance or training before the accident. Since 2007, it had accumulated 2,997 hours and 1,359 cycles on contract, and 3,507 hours and 1,877 cycles total.
Maintenance records since 1990 showed compliance with FAA Airworthiness Directive (AD) 89-25-10, requiring inspection of wing lower forward spar attach fittings, center section, and outboard wing spar caps. Sixteen wing spar inspections were performed since AD effectiveness, including six since 2007. Annual spar cap visual inspections were done 16 times since 2007.
During a scheduled inspection months before the accident, a certified NDT technician found a crack indication in a fastener hole on the left wing's lower forward spar cap at the wing root. The hole was oversized but still showed a crack. FEA's maintenance provider, Falcon Air Service (FAS), submitted a report to Textron Aviation in April 2021. Textron responded that the crack necessitated replacement of the center section forward spar cap, center section forward lower fittings, and both outboard main spar assemblies, referencing SIRM 57-13-01 warnings.
FEA and FAS elected to repair rather than replace. The facility owner contacted an FAA Designated Engineering Representative (DER) for a repair design. The repair involved oversizing the hole and installing an external doubler. It was completed and signed off in May 2021 with FAA Form 337 and Form 8110-3 from the DER. The DER claimed no knowledge of the Textron communications; FAS claimed otherwise.
A subsequent eddy current inspection by a Level II NDT inspector, certified per NAS 410 and holding an FAA repairman certificate, showed the repair successful. The inspector had performed EC/FPI inspections on King Air airplanes six times between December 2020 and July 2021.
Textron's Structural Inspection and Repair Manual (SIRM) 57-13-01, at revision D2, provided inspection intervals and instructions. It included warnings that a crack in the center section lower forward spar cap requires replacement of all lower forward inboard fittings, the lower forward spar cap, and both outboard forward wing panel main spar assemblies. An Alternate Method of Compliance (AMOC) was not sought for the repaired crack.
The Wichita Aircraft Certification Office (ACO) stated that a DER-approved repair, though FAA-approved, was not done in compliance with AD 89-25-10 because instructions were not provided by Beech. However, an AMOC would likely have been approved. The ACO considered it a technical noncompliance rather than an airworthiness issue.
Meteorological Information
No significant weather was indicated over northern Arizona at the time. The nearest METAR reported clear conditions, 10 statute miles visibility, wind 260° at 11 knots gusting to 18 knots. No active AIRMETs, SIGMETs, or PIREPs were reported.
Wreckage and Impact
The airplane impacted a ridgeline in mountainous desert terrain. The main wreckage was mostly consumed by post-crash fire, with debris scattered over several acres. The left wing separated outboard of the nacelle and was found 0.79 miles northeast, without thermal damage.