Helicopter MRO

A great example of an MRO partnering with an OEM on a specialized repair/modification project, and providing AW139 operators an alternative to extensive downtime, Heli-One is currently offering a tailboom exchange program, where an operator can exchange...

The AgustaWestland AW139 is a very successful medium-sized aircraft that has reliably secured its role in the world of helicopter operations. But, like many new aircraft types that experience teething problems after introduction to service, the AW139 has had to face this challenge, specifically with issues relating to its tailboom. However, Heli-One, a large helicopter MRO located in Delta, British Columbia, Canada, is working with the OEM on an interesting tailboom repair and replacement program.

The AW139 is a conventional twin-engine medium size transport helicopter, powered by two Pratt & Whitney PT6C-67C turboshaft engines which drive a five-blade fully articulated main rotor system and a four-blade tail rotor. The first AW139 flew in February 2001 in Italy and the first customer aircraft was delivered in 2003. The AW139 helicopter is successfully used in a variety of roles including emergency medical service, law enforcement, executive transport, search and rescue, maritime, and offshore oil and gas operations.

On Aug. 25, 2009 an incident occurred involving an AW139 operated by Gulf Helicopters in Doha, Qatar. During the taxiing phase the aircraft experienced a structural problem with its tailboom. No one was hurt as a result of this event.


Prior to the Qatar event operators started to report debonding of the tailboom’s lateral panels. On Aug. 27, 2008, European Aviation Safety Agency (EASA), alongside AgustaWestland issued an EASA AD 2008-157 for inspection to detect debonding of the panels by tap-hammer within 100 flight hours, then at 300-flight hour intervals. The inspection was performed in accordance with Agusta Bollettino Tecnico (Technical Bulletin) BT139-134.

In reaction to the Qatar event, on Sept. 4, 2009, EASA AD 2009-198-E was issued which superseded AD 2008-157. This AD reduced the inspection interval to a 25-flight hour or 30-day initial inspection interval, and a 50-flight hour recurring inspection to be completed in accordance with BT139-193. Some specific aircraft serial numbers had the initial inspection reduced even further to a five-flight hour initial inspection in accordance with BT139-194.

Less than two months later on Oct. 28, 2009, EASA AD2009-234-E was issued to supersede AD2009-198-E. One day later it was revised to the now currently and still applicable EASA AD2009-234-E R1, in order to change serial number applicability in one section of the initial issue of the AD.

This latest AD changed the inspection requirements to include a daily general visual inspection of the tailboom right hand side skin. The tap-hammer inspection remained at 50-flight hour intervals for most aircraft, except a few tailboom part number and aircraft serial number combinations. Aircraft fitted with these tailbooms had the inspection interval reduced to 25 flight hours.

All the inspections called out in EASA AD2009-234-E R1 are to be accomplished in accordance with BT139-195 Rev. B. At this time, any defects found that are beyond the set limits must be reported to the manufacturer. Repair schemes are created by AgustaWestland product support engineering department on an aircraft by aircraft basis.

Tailboom construction

The construction of the tailboom assembly consists of two separate pieces, the tail cone and the vertical fin. The tail cone is between STA 8,700.09 mm and STA 11,020.0 mm, and includes two lateral bonded sandwich-panels having aluminum skins and nomex honeycomb core, a bottom sandwich-panel of the same construction, a front aluminum frame, and six short longerons, attached to the lateral panels and to the front frame. Six fittings with bolts attached to the short longerons connect the tail cone to the fuselage.

The vertical fin is attached to the tail cone at STA 11,020.0 mm and extends aft from STA 11,020.0 mm to STA 13,349.3 mm. The vertical fin includes the frame at STA 11,020.0 mm, the front and rear longerons, and a top rib and middle rib with attachment points for the tail gearbox, intermediate gearbox, and horizontal stabilizer or ”tail-plane.”

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