Re-lifing a Turboprop aircraft exhaust 

MSM aerospace fabricators specialises in aircraft MRO (Maintenance, Repair and Overhaul) through its EASA 145 approved specialist facility.  Based in the North West of England, on the outskirts of Manchester, MSM is only 10 miles/16 kms from Manchester International Airport. From here we service numerous airlines including budget, regional and  international, as well as other MRO aerospace organisations.

MSM’s MRO work covers a wide spectrum of aircraft parts, from simple weld repairs of bleed air ducts and hydraulic reservoir’s mounting brackets to more complex full overhauls of air intakes which have suffered bird strike damage. MSM has developed a specialist skill in not only repairing aircraft exhaust jet pipes but also re-lifing them.

One example of re-lifing an aircraft exhaust is the BAE Jetstream 41 turboprop. These aircraft are typically used as a regional airliner carrying up to 30 passengers on relatively short hops. Over time, and primarily as a result of vibration and heat fatigue, the main engine mounting flange, the exhaust’s support brackets and localised areas of the body of the exhaust itself become worn, chaffed and split. This eventually leads to these features of the exhaust requiring repair.

Fig. 1 This shows typical cracks and wear  

 

A simple solution is to perform these repairs by removing the problem area/attachment and welding in a new section i.e. a patch repair. However this may only provide temporary relief, as soon after entry back into service other areas of the exhaust may soon also require replacement and repair. As every repair means disturbing or removing the exhaust’s heat insulation jacket, it can be damaged,  leading to high costs to replace. Also the concern is that if an exhaust has undergone numerous patch repairs the whole structure can be weakened.

Fig. 2 This shows numerous patch repairs around the top support bracket

MSM has resolved this problem and effectively re-lifed the exhaust by replacing complete sections of the exhaust and its mounting flange with new. As well as keeping the aircraft exhaust in service for a much longer period, it is a much more robust solution and also much more cost effective than repeated small repairs. The Jetstream 41 exhaust is approx. 2m long x 350mm diameter with the tube material being 0.5mm thick stainless steel. It is made up of three sections, the bottom section consisting of the machined engine mounting flange ring, the longer middle section, and the top section which has a mounting bracket support ring and other support flanges.

Over time, these areas of the support ring/brackets often show signs of wear and chaffing which results in the spotwelds becoming cracked. The exhaust tube itself can become cracked and split on either side of this support bracket. And the main mounting ring also suffers the same symptoms. The obvious danger is that the exhaust breaks or becomes loose whilst in flight.  Another problem is that the exhaust fumes leak through these cracks.

MSM has, with the authority of BAE, devised a Repair scheme which not only solves these problems but gives the exhaust a new lease of life. This involves replacing the top of the middle section tube and the whole of the top section tube with completely new sections; these sections have a brand new mounting bracket support rings, channels, doublers and “Z” member support brackets.

All of these new parts are manufactured in-house, with the two new main tube sections being rolled into tube from flat sheet material and then Jetline fusion seam welded along the joint line.  The other parts are formed to size and then resistance spot welded and/or TiG welded to the new tube sections. The new tube sections are then resistance seam welded together and then welded to the remaining original main body.

Fig. 3 This shows the complete new end section

This repair scheme also involves replacing the bottom section’s mounting flange with a new flange machined from forging, which is also resistance seam welded to the original section.

To complete the process MSM then PFD dye penetrant inspects all of the welds prior to fitting a new insulation jacket. The result is an exhaust jet pipe which is virtually as good as new; all completed in a six week time frame and with EASA’s Form 1 release.

 

Fig. 4 This shows the completed re-lifed exhaust

The above procedure is endorsed by MSM’s AS9100 rev C accreditation, NADCAP approved welding and NADCAP approved PFD facilities, and EASA Form 1 release. It highlights MSM’s 75 year heritage in the Aerospace industry using our specialist knowledge and capabilities to provide innovative cost effective solutions and efficient service.

MSM handles many different types of aircraft fabrication repairs and we particularly specialise in weld repairs, either TiG or resistance, in Inconels, Titanium, stainless steels and aluminium alloys. We undertake to survey your damaged part/assembly, produce a detailed recommendation and cost report, and source the authorised Repair scheme from the OEM (original equipment manufacturer). MSM offers an AOG service for those most urgent repairs.

If you need more information or you would like us to get in touch to discuss a specific requirement please complete the contact us sheet.