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 tailboom modification

There are two technical bulletins, BT139-159 Rev. B, and BT139-200, currently issued by AgustaWestland that strengthen the tailboom structure. These two bulletins are fully compatible with each other and can be applied together to the same tailboom in order to achieve maximum tailboom strength.

After operators had started reporting debonding of the tailboom panels but before the event in Qatar, AgustaWestland issued a technical bulletin BT139-159. This bulletin is aimed at improving the structural strength of the tailboom by replacing the original two lateral sandwich-panels with new bonded panels having aluminum skin and aluminum honeycomb core. The weight and balance changes for this bulletin are negligible and so far AgustaWestland is keeping this bulletin optional.

After the event in Qatar the second bulletin, BT139-200, was issued. This bulletin consists of four longeron reinforcement or extensions to be installed on both the upper and lower right and left hand sides to extend the existing longerons from STA9140 mm to the STA 11,020 mm butt splice that attaches the vertical fin to the tail cone. With the extensions installed, the longerons extend the complete length of the tail cone assembly greatly improving its strength.

This bulletin however comes with a weight and balance price. Eighteen kilograms is added at an arm of 10,081 mm shifting the center of gravity aft. On the long nose AW139 this is of no concern, however it may cause some hesitation on the short nosed aircraft depending on its configuration and operations. Carrying out BT139-200 eliminates the inspections called out in BT139-195 Rev. B as it is now not applicable. Performing BT-200 can be done on its own without removing the tailboom from the aircraft; however, paint damage will be done to the tailboom.

Performing BT139-159 Rev. B requires a need for a full shop with specialized tooling and technicians. The tailboom must be removed from the aircraft and disassembled using specialized tooling, a jig, and a holding fixture for reassembling the tailboom parts.

This project requires several technical experts familiar heavy structural repairs and with the AW139, the tailboom history. There are three of these fixtures in the world, only two of them are currently in operation. One is located at AgustaWestland in Italy, and one at Heli-One in British Columbia, Canada. Heli-One has a dedicated crew that has visited the Italian facility for specialized training to perform this work. Panel replacement also will require a painting facility in order to restore the paint scheme on the tailboom. Considering the tailboom must be removed from the aircraft for this bulletin, it is recommended that BT139-200 is also performed at this time.

The labor hours required will be reduced by performing the two bulletins together, and the tailboom will only need to be repainted once. Performing both bulletins is ideal to obtain the strongest possible tailboom structure. Tailboom removal can be accomplished using an overhead hoist and sling. When the tailboom is being removed for replacement, it is recommended that it be removed “undressed” of all components, wiring, and plumbing before tailboom removal. Document this by taking pictures of the removal of the wiring harnesses as it helps when it comes time to lay them out in the new panels. Once everything is stripped from the tailboom it will be very light and will make removal very easy. It is a very manageable 73 Kg.

Removing the tailboom in order to accomplish BT139-159 Rev. B will cause extensive downtime, especially once you factor in shipping to a facility with the proper tooling, modification of the tailboom, paint, and return shipping. This is 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.

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