Engines

Cracked Compressor Scroll

ALLISON, 250-C47B
SERVICE DIFFICULTY REPORT
(SDR) # 20120229008

SDR submitted:

An approximately 10 cm (4 inch) vertical crack was found on the left forward side of the engine compressor scroll during a scheduled daily inspection. The engine was completely replaced. The compressor was sent for overhaul. The scroll was a thin-wall type and will be exchanged for a thick wall version

Cracked compressor scroll

Transport Canada Comments: 

Cracks are common with the thin wall compressor scroll. The cracks in this area are easy to detect and if large enough will cause an increased turbine temperature and likely a degradation of performance. Operators are reminded to be aware of this potential.

Auxiliary Power Unit Fire Warning in Flight

BOMBARDIER, EQUIPMENT
SDR # 20120227003

SDR submitted:

While the aeroplane was climbing through 10 000 feet with auxiliary power unit (APU ) operating, the red indication & crew alerting system (ICAS ) “APU fire” posted. Crew selected the APU fire switch to shutdown the APU and message cleared. Crew declared an emergency and returned to the departure airport. An investigation revealed no sign of a fire.

The operator reported that this was the 7th occurrence on this aeroplane. The first occurrence initially took place around 2005 and was not reported. Also, at that time in an effort to save on fuel, a change in procedure had the crew shut off the APU prior to flight, thus the situation remained dormant until recently whereby crew now operate the APU in flight.

An inspection indicated that sealant inside the APU compartment was missing at the seams and at the APU mount to firewall interface. This resulted in lower pressure within the APU enclosure and may have resulted in reduced APU eductor efficiency. This caused the APU exhaust gases to be sucked into the APU enclosure tripping the fire loops.

Sealant was applied to the missing areas and the aeroplane flown with the APU running. Checked serviceable.

 Photo 1: APU enclosure missing sealant. Arrows pointing at missing sealant.
Photo 2: APU enclosure with sealant. Arrows pointing at good seals.

Transport Canada Comments:

This is an unusual instance, but a good example of where a problem can be dormant, only to reappear at a later point. Any abnormal occurrences must be dealt with appropriately and thoroughly.

Cracked Fitting On Propeller Governor

GARRETT, TPE331-11
SDR # 20111118015

SDR submitted:

During the daily inspection, it was noted that oil was leaking out of the left engine cowling. Upon investigation, a fitting on the left engine propeller governor was found cracked. The fitting was replaced and the aeroplane was returned to service.

Cracked fitting.

Transport Canada Comments:

Oil leaks can sometimes be an indicator of major problems. What may appear to be a minor leak can actually be an indicator of an impending failure which can lead to an in flight shutdown.

Cracked Spinner Cone Causing Fan Blade Damage / in Flight Shut Down

GENERAL ELECTRIC, CF34-10E5A1
SDR # 20111202002

SDR submitted:

While at flight level 320, the crew reported high engine vibrations on the number 2 engine. They reduced power on the engine to idle to reduce/stop the engine vibrations. They declared a pan pan emergency and returned to departure airport where they landed overweight by approx 3000-4000k. After landing, the crew inspected the engine and found damage to several fan blades due to a missing segment of the engine nose cone.

Damage to spinner cone.

Transport Canada Comments:

This issue may have been caused by pre-existing cracks prior to re-work in accordance with service bulletins 72-0159 and 72-0186. Maintainers are urged to become familiar with the contents of these bulletins.

Fractured Bleed Air Line Causing Fire Warning

PRATT & WHITNEY-USA, JT8D-9A
SDR # 20120319011

SDR submitted:

After takeoff, climbing through 6000 feet #2 engine fire warning activated. Crew followed the check list and returned with #2 engine shut down. Inspection of the engine found no evidence of fire however a ruptured bleed air duct was discovered. The duct was repaired and the aeroplane returned to service.

 Circle is showing cracked bleed duct.

Transport Canada Comments:

As aeroplanes age, special attention must be given (during inspections) to components that are subjected to high heat and vibration loads.

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