Agusta A109 near Salt Lake City, UT — 2019-11-13

Probable cause

The flight nurse’s inadvertent application of left anti-torque pedal during cruise flight, which resulted in a rapid yaw and pitch movement that caused the tail rotor blades to contact the tailboom.

NTSB narrative

The crew of the helicopter air ambulance flight departed to pick up a patient in night visual meteorological conditions. While en route to their destination, a flight nurse, who was seated in the left seat and communicating with ground personnel, inadvertently depressed the helicopter’s left anti-torque pedal instead of the foot-activated push-to-talk (PTT) switch to activate the microphone. The helicopter suddenly yawed left about 11°, which the pilot immediately countered and restored straight-and-level flight. The helicopter sustained damage to the tail rotor blades and empennage that was not discovered until several hours later when the accident crew was relieved. The damage to the blades and empennage was consistent with their making contact, and the flight data suggest this occurred during the first leg of the shift flight as the crew did not experience any other events that would have caused the degree of damage observed. Postaccident examination of the tail rotor gearbox and tail rotor blades did not reveal any anomalies. A performance analysis by the helicopter manufacturer showed that the amount of left pedal applied at the time of the pilot’s yaw recovery exceeded the parameters tested during certification. The flight nurse seated in the cockpit at the time of the accident normally sat in the rear cabin and was likely not as familiar with the location of the PTT, especially in nighttime lighting conditions.

Analysis

Primary failure mode

Human factors

First missed decision gate

Flight nurse should have used the PTT button instead of the anti-torque pedal.

NTSB coding

• Inflight upset · Enroute

Evidence available

• Photos
• 14 docket documents

Docket documents14

• ACCIDENT FLIGHT OPERATIONS COMPLIANCE FORMform
• AIRCRAFT PERFORMANCE STUDYform
• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1form
• RELEASE OF AIRCRAFT WRECKAGE, NTSB FORM 6120.15form
• STATEMENT OF PARTY REPRESENTATIVES TO NTSB INVESTIGATIONinterview
• ADULT FLIGHT NURSE OPERATOR TRAINING RECORDSother
• BRIEFING ACRONYMSother
• EMAIL CORRESPONDENCE WITH OPERATORother
• EXCERPT FROM GENERAL OPERATIONS MANUALother
• N271HC SCHEDULE NOVEMBER 12 - 13other
• RECORD OF CONVERSATIONSother
• ACCIDENT PHOTOGRAPHSphotos
• HELICOPTER SPECIALIST REPORTreport
• MATERIALS LABORATORY FACTUAL REPORTreport

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