Air Ambulance B407 Hospital Helipad Deck Edge Tail Strike During Shallow Approach (N947LH)
On the afternoon of 22 January 2019 Executive Air Taxi Corp Bell 407 N947LH, an air ambulance operated for Trinity Health‘s NorthStar Criticair service, suffered a tail strike during a landing at the Trinity Medical Helipad (2ND4) near Minot, North Dakota. The pilot was uninjured, but the helicopter sustained substantial damage.
The Accident and Safety Investigation
The US National Transportation Safety Board (NTSB) explain in their safety investigation report (published 5 May 2021) that the aircraft was due to pick up a medical crew and was operating a Part 91 positioning flight.
The pilot [6341 hours total, 98 on type] stated he performed a right 180° circling approach to the helipad.
The helipad was on top of a 5-storey hospital building.
“Enroute I punched up ATIS on the radio to confirm winds and they were NW (300 degrees) winds at 7 knots. So I flew over the big church (northeast of the pad a couple of blocks) and then performed a 180 right circling approach to the pad”. As he finished the turn, he thought he was a little low on final approach and “pulled in a little collective.” He applied more collective as he was levelling off and the “helicopter contacted the pad firmly.”
The pilot added that it was firmer than a normal landing, but he thought everything was okay until he noticed a small vibration.
Before departing with the medical crew, the pilot still felt the vibration in the helicopter, so he shut the helicopter down to check. After shutdown, the crew walked toward the tail and noticed a slight bend in the lower vertical fin, the tips of both tail rotor blades missing, and the helipad safety fence [i.e. the helideck perimeter netting] was missing a small section of the fence-edge pipe.
Subsequent examination of the helicopter identified surprisingly large cracks in the tailboom structure. The helicopter was removed by crane.
NTSB Probable Cause
The pilot’s failure to maintain clearance from fencing around the landing pad during landing, which resulted in the tail rotor contacting the fence.
But What About Flight Data Monitoring?
Oddly, there is no mention of the any flight data being analysed. Data can usually be extracted from GPS units for example if investigators are minded to make an effort. However, the FAA changed Part 135 in 2017 so that helicopter air ambulance operators had to comply with a new Flight Data Monitoring (FDM) System requirement, FAR 135.607:
After April 23, 2018, no person may operate a helicopter in air ambulance operations unless it is equipped with an approved flight data monitoring system capable of recording flight performance data.
FAA AC 135-14B Helicopter Air Ambulance (HAA) Operations explains that:
The FDMS should record digital or analog raw data, images, cockpit voice or ambient audio recordings or any combinations thereof which ideally yield at least the following flight information: • Location; • Altitude; • Heading; • Speeds (airspeed and groundspeed); • Pitch, yaw, and roll attitudes and rate of change; • Engine parameters; • Main rotor RPM; • Ambient acoustic data; • Radio ambient audio; and • Any other parameter the operator deems necessary (e.g., high definition video recording looking forward including instrument panel and forward cockpit windshield view, intercommunications system (intercom) between pilot and medical crew, communications with air traffic control (ATC), OCS, base operations, first responders at scene, hospital, etc.)
So while this sector was classified as a Part 91 positioning flight, its very next flight would have required a suitable FDM System. It would be very unusual to have planned to turn the system off for sectors it was not legally required.
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