History of the Flight
On November 16, 2019, at approximately 1845 eastern standard time, a Leonardo A109E helicopter, registration N901EM, experienced a severe inflight vibration and subsequently executed an emergency landing near Penobscot, Maine. The helicopter was registered to LifeFlight of Maine LLC and operated by SevenBar Aviation. The flight was conducted under 14 Code of Federal Regulations Part 135 as a helicopter air ambulance. It had departed Blue Hill Memorial Hospital in Blue Hill, Maine, and was en route to Eastern Maine Medical Center in Bangor, Maine after loading a patient. About five minutes into the flight, the pilot reported feeling a “small vibration” on the flight controls, fuselage, and seat. The vibration was characterized as a lateral shake. The pilot reduced collective and slowed the helicopter's airspeed, and discussed the vibration with the crew. The vibration subsequently increased in severity, prompting the pilot to immediately perform a precautionary landing. The helicopter landed successfully, and no injuries were reported among the four occupants.
Damage to the Helicopter
A postlanding examination revealed that one of the four main rotor blade tip caps exhibited a fracture along its leading edge, approximately 18 inches in length, with the upper skin separated from the core and lower skin. This main rotor blade was identified by part number (P/N) 709-0103-01-109 and serial number (S/N) L265. A subsequent examination found a second main rotor blade tip cap with a crack about 1.25 inches long along its leading edge. That blade was identified as P/N 709-0103-01-109 with S/N L251. Both main rotor blades were removed and sent to Leonardo facilities in Broussard, Louisiana for further examination.
Test and Research
On January 7, 2020, representatives from the National Transportation Safety Board (NTSB), Leonardo Helicopter Division, and SevenBar Aviation convened at Leonardo facilities to examine the two main rotor blades. No anomalous damage other than the tip cap cracks was observed. The tip cap on blade S/N L265 was identified as P/N 709-0103-29-109, S/N L206; the tip cap on blade S/N L251 was P/N 709-0103-29-109, S/N L232. The tip caps were removed and sent to the NTSB Materials Laboratory in Washington, D.C., for examination.
The tip cap is constructed of two preformed steel shells (upper and lower skins) bonded to an aluminum honeycomb core. The skins are welded at the leading edge and bonded at the trailing edge. The assembled tip cap is bonded to the main rotor blade and secured to the blade spar with screws.
Metallurgical examination of the 18-inch fracture on tip cap S/N L206 revealed it was adjacent to the weld along the lip of the leading edge. The fracture exhibited signatures consistent with multiple initiation fatigue cracking, emanating from the internal edge of the lower surface at the toe of the weld. No evidence of weld defects was found. Examination of the 1.25-inch fracture on tip cap S/N L232 showed similar characteristics. The material composition of both tip caps was consistent with manufacturer specifications.
Additional Information
Main Rotor Blade History
The incident helicopter, airframe S/N 11614, had both main rotor blades (S/Ns L251 and L265) installed new in July 2004 at the time of manufacture. They remained installed until October 18, 2012, when both blades were removed at an aircraft total time (ATT) of 5,527.9 hours for erosion repairs. Both blades were reinstalled the same day. At the time of the incident, the airframe had an ATT of 10,078.4 hours, and each blade had a component total time of 10,078.4 hours.
Inspection Requirements
At the time of the incident, a main rotor blade tip cap inspection was required every 50 hours and could be found in three documents: Federal Aviation Administration (FAA) Airworthiness Directive (AD) 2007-26-52, dated May 9, 2008; Leonardo Helicopter Division Bollettino Tecnico (BT) No. 109EP-85; and A109E Maintenance Manual Section 05-50. The AD required a visual inspection of the tip cap leading edge for cracks using a 10x or higher power magnifying glass. If a crack was suspected, a dye penetrant inspection was required. If a crack was found, the blade had to be removed and replaced.
Inspection History on N901EM
The helicopter had accumulated an ATT of 10,078.4 hours and began the day at 10,077.2 hours. The last compliance with AD 2007-26-52 and the 50-hour tip cap inspection was recorded on November 8, 2019, at an ATT of 10,065 hours—approximately 13.4 hours before the incident. The mechanic who performed the inspection reported no defects and no distractions or time constraints. Subsequent entries on November 3 and October 23, 2019, also showed AD compliance. The operator's assistant director of maintenance stated that both 25-hour and 50-hour inspections were performed at each compliance entry, regardless of time remaining. He noted that dye penetrant inspections were uncommon, and he could not recall one being performed in the past four or five years across the operator's fleet of four A109-series helicopters.
History of A109 Tip Cap Cracks
Past tip cap cracks and separations led to the issuance of FAA AD 2001-24-07 R1, effective July 30, 2004, which instituted a recurrent 25-hour inspection. Replacing affected blades with those having airworthy tip cap P/N 709-0103-29-109 was a terminating action. Two subsequent incidents involving cracks or fractures on P/N 709-0103-29-109 tip caps led to FAA emergency AD 2007-26-52, which superseded the earlier AD. Since then, there have been six occurrences worldwide of partial or complete inflight separation of the P/N 709-0103-29-109 tip cap, including this incident.
In June 2016, a composite tip cap, P/N 709-0103-46-101, was certified by the European Aviation Safety Agency (EASA) and is not subject to the recurrent 25-hour and 50-hour inspections required by AD 2007-26-52.
Post-incident Actions
On December 6, 2019, SevenBar Aviation issued an internal maintenance bulletin requiring a daily tip cap inspection on all A109E main rotor blades, regardless of tip cap part number.
On October 19, 2020, Leonardo issued Revision A of BT No. 109EP-085, which replaced the visual inspection with a dye penetrant inspection every 50 hours. EASA issued AD No. 2020-0230 on October 22, 2020, to reflect these changes. At the time of the report, the FAA had not yet released an analogous update to AD 2007-26-52.