(Hand flying blind) Cessna citation breaks apart after Severe 36000 FPM DIVE

Cessna Citation N711BX: Loss of Control and In-Flight Breakup

At 9:50 a.m. local time on 18 January 2016, Cessna 525 N711BX departed Salt Lake City International Airport for Tucson, Arizona, on a personal cross-country flight. The aircraft was being operated under Part 91 with an IFR flight plan. On board were an airline transport-rated pilot and one passenger. About two minutes into the flight, the crew's routine climb changed into a rapidly developing avionics and control problem.

At 09:51:59, the pilot reported climbing through 7,500 feet. ATC cleared the aircraft toward FL230 and subsequently instructed it to maintain 14,000 feet. At 09:55:01, the pilot reported a failure involving the flight management system and said he was switching navigation modes. Shortly afterward, the pilot reported an autopilot failure and asked to climb toward visual conditions.

The controller continued providing headings and altitude instructions. The pilot said he was trying to reach clear skies and later stated that he was hand-flying the airplane. The aircraft was also experiencing an altitude-reporting problem. ATC warned about traffic above and offered vectors around precipitation. At 09:57:12 the pilot said he was heading to Tucson, that his altitude would not hold and that he was hand flying.

At about 09:57:20 the aircraft began turning away from its established southerly course without an ATC clearance for the turn. The controller advised the pilot of the deviation and continued offering vectors. The pilot then declared MAYDAY and said he was losing instruments and wanted to get clear of the weather. ATC cleared him higher, first toward FL230 and then toward FL310. The pilot acknowledged the climb but reported difficulty dialing the assigned altitude into the system.

The aircraft reached about 21,300 feet while continuing a right turn. At 09:59:13 the controller observed the right turn and asked whether the pilot could turn left. The pilot replied that he was trying to climb. About thirty-four seconds later, ATC reported losing the aircraft's altitude readout. There were no further transmissions. Between 09:59:49 and 09:59:58, radar showed the aircraft descending from 21,300 to 16,000 feet, with the descent rate increasing from 9,600 to approximately 36,000 feet per minute.

The aircraft subsequently broke apart in flight. The wreckage was spread over a debris pproximately three-quarters of a mile long and one-third of a mile wide. Witnesses reported hearing explosions or booms and seeing debris, including debris that appeared to be on fire. An FAA inspector who attended the site reported no visible ice accumulation on the wreckage, although snow was falling at the site.

The NTSB examined the aircraft's flight instruments and found no evidence that could establish exactly what instrument anomalies the pilot had experienced before the loss of control. The report noted that the airplane had three separate sources of attitude information and that simultaneous failure of all three was considered unlikely. The investigation also found no pre-existing structural or engine condition that explained the breakup; structural fractures were consistent with overload.

The final investigation concluded that the pilot lost control because of spatial disorientation while operating in instrument meteorological conditions, leading to exceedance of the airplane's design stress limits and an in-flight breakup. The reported instrumentation anomaly was identified as a contributing factor, but its origin could not be determined.

The event is therefore not accurately described simply as an unexplained 36,000-fpm dive. The NTSB established a sequence in which reported avionics problems, a high-workload single-pilot cockpit, instrument meteorological conditions, increasing deviations and loss of control culminated in structural breakup. The investigation also made clear that the precise origin of the reported instrument anomalies remained unresolved.

At 09:57:06 the controller asked the pilot to describe where he believed the clearest skies were so that vectors could be provided. The pilot said he was heading toward Tucson and that his altitude would not hold. He was hand flying. Radar then showed a right turn away from the established southerly course. The controller instructed him to fly his present heading and advised that the precipitation would clear in about four miles. The pilot subsequently declared MAYDAY and said he needed to climb higher because he was losing different instruments.

At 09:58:01 the controller cleared the aircraft to FL230, then amended the clearance to FL310. The pilot confirmed the climb but soon said he could not dial the altitude into the system and would read it out to ensure his second system was working. At 20,700 feet the controller issued a no-gyro left turn for vectors toward the southeast. Radar instead showed the aircraft continuing a right turn. It reached approximately 21,300 feet at 09:59:12.

Instrument testing did not identify the source of the anomalies reported by the pilot. The NTSB noted that the aircraft had three separate attitude-information sources powered independently, making simultaneous failure of all three unlikely. The standby attitude indicator and standby compass would have remained available for aircraft control and heading information. The report also noted that the pilot was operating alone in a high-workload environment without another crewmember to share the task.

The pilot held an airline transport certificate and was qualified for single-pilot CE-525 operations. His records showed 3,336 hours total flight time, 3,138 hours as pilot in command, 1,588 hours of turbojet time and all of that turbojet time in the accident airplane. He had also completed recurrent CE-525 training in August 2015. These qualifications did not prevent the rapid deterioration of the flight once the reported instrument and autopilot problems combined with the weather and high workload.

Accident Facts

Sources

• Video source (ATC/audio reconstruction)
• NTSB, Final Report WPR16FA054.
• NTSB Docket WPR16FA054, including ATC transcript and examination reports.
• Aviation Safety Network, N711BX accident record.
• Video/ATC recording