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August 2015

FIXED WING

Diamond DA42: Austro E4 - 07/08/2015 (201511182)

Between April and July 2015 there have been several reports of 'Coolant Low Level' annunciated for RH Engine (some extinguished on landing, some illuminated before flight aborted).  Coolant residue was occasionally found around the Pressure Relief Valve suggesting venting action.  Coolant level was low and replenished.  Pressure testing of the coolant system was carried out with no leak evident.  Ground runs were performed with no findings. Several troubleshooting actions were completed, in consultation with Airframe and Engine Manufacturers but symptoms persisted.  It was found that the coolant system remained marginally pressurised after a 'cool down' period (a weekend on one occasion).  It was also noted that the LH Engine remained pressurised (though less so) after the same cooling period.  (Approx 500ml fluid was expelled when coolant tank caps were removed). With manufacturers advice, the RH Cylinder Head was removed. There was evidence of Head Gasket breach via heavy machining marks on the engine block/gasket mating surface.  When the LH Cylinder head was removed, similar marks were found.  Both engines are currently being replaced. 

Grob G115: Lycoming O-360: Wittering - 06/08/2015 (201510832)

Shortly after take-off, during checks at 2000', shortly after take-off, the fuel flow was set to 56 l/hr iaw placard.  Passing approx 4000', in the climb, the fuel flow was noted at 65l/hr which is abnormal. The Fuel flow was then observed to smoothly fluctuate between 65 and 45 l/hr. Aircraft was turned for potential return whilst continuing to climb. Shortly after turn, passing 4800' with full power set, the fuel flow was seen to be fluctuating between 25 and 35 l/hr, the engine began to 'rough run' with associated banging/popping and vibration.  Rough running drill carried out with no improvement.  PAN declared with the intention of positioning for a Precautionary Forced Landing.  Engine banging/popping and vibration intensified and at approx 3nm to run to ‘High key ‘at approx 4000' the RPM decayed to a 'windmill' speed.  Having already conducted the rough running drill the throttle was retarded to idle and slowly advanced to attempt restart engine did not respond but continued to windmill.  Engine Failure (Mechanical) drill actioned to ensure engine was safely shut down. MAYDAY declared. AC landed safely with propeller continuing to 'windmill until just before touchdown. LAE briefed and undertook investigation on 07 Aug 15.  Confirmed engine driven fuel pump had failed, leak from case drain.

Engine replacement completed 18 July 15 (Due to TBO) Engine bedding in completed.  Engine reported to have stopped on taxi-in on 20 July 15 and ran erratically on 21 July 15, fluctuating RPM 1800-2100 during mag checks on 06 Aug 15, performance parameters within limits.  No evidence of rough running despite prolonged ground run.  Found failure of the engine driven fuel pump, providing erratic fuel flow, unit replaced. Defective pump returned.  Quality issue with manufacture of the pump. The manufacturer had already raised a Bulletin instructing replacement of certain suspect units manufactured during 2014, but this unit fell outside the Bulletin criteria.  It has now been re-issued to extend the scope of units to be replaced.    

Piper PA28:  Lycoming O-320: Chichester/Goodwood - 14/06/2015 (201508372)

After a normal approach and landing on Runway 32, the regular, high-time hirer vacated right to taxi to parking. He noticed the left toe brake seemed to have excessive movement and was unable to complete a 180 degree turn left using differential braking.  He requested shutdown in present position in order to investigate. It was then discovered that the left brake caliper was detached from its fixings at the end of the oleo strut.  Engineering found bolts securing the caliper had sheared.  New set of brake linings (pads) were noted which are believed to have been damaged from the occurrence.  Engineering supplied brake assembly components including new bolts and brake linings(pads).  

Piper PA42 Cheyenne: P& W PT6: Oxford/Kidlington - 18/08/2015 (201511350)

Four nacelle upper engine mount attachment bracket assemblies cracked to varying degrees.  Found by visual inspection and confirmed by dye method.  Subsequent to the findings, fleet checked and similar incidence found on 2 A/C. Grounded for investigation.  

SINGLE ENGINED ROTARY WING 

Bell 206: Allison 250: Compton Abbas  - 15/08/2015 (201511457)

Drag pin assembly surrounding plate found damaged.  1st Observation: At approximately 14:40 local time, after a rotors running passenger changeover, the aircraft was at ground idle. I started spooling it up to flight RPM. I noted the torque at around 40%. I then momentarily noted the torque exceeding 40% but certainly no more than 50% to which I closed the throttle slightly to maintain 40% whilst bringing the aircraft up to flight RPM. It was at that point I heard a somewhat loud pop, similar to that of a piston engine back firing; I noticed the needles on a few gauges increase rather rapidly, I also experienced a yawing motion at this point. I quickly shut the throttle down to the idle position, and noted the gauges were all back and in their normal positions with no indication of a problem. It's hard to say as to whether or not the yawing was a direct result of the loud pop, or more to do with the rapid closure of the throttle to the idle position. Later that evening a ground crew member mentioned seeing a "small puff of smoke" leave the exhaust at the time of the pop. Observation 2: This second observation may or may not be related to the first. At about 17:15 local time, I conducted a post-flight/A-Check and discovered the metal plate surrounding the drag pin assembly had a section of it as well as 3 rivets missing. There had been no hard landings nor abrupt control movements during the day, no knocking nor any vibrations, nothing during the day that would lead me to suspect that occurring. I spoke to the ground crew to see if they witnessed any hard landings, however none could recall any hard landings during the day.

Hughes 369: Allison 250: Northampton/Sywell - 10/12/2014 (201418426)

During routine maintenance the build records from previous repair shows all assembly limits/checks and build procedure to be correct. The post repair test-run log shows all recorded vibration readings within allowable limits. The disassembly findings during this investigation did not find any anomalies relating to assembly of the compressor or any limits out of parameters. The front support was sent to an external company for independent analysis. This analysis concluded the boss detached due to vibration fatigue. The no2 bearing was found to have :-fretting to outer race thrust face/assembly witness marks to inside diameters of inner races / heavy internal wear to retaining ring ball pocket diameters. Cause unknown. After reviewing a number of compressor test results and comparing the vibration indication at 420 SHP, an average reading is approximately 0.35 IPS. During the post repair test under project 6481037 the vibration recorded at 420 SHP was 0.53 IPS / limit 0.6 IPS. In conclusion maintenance has not been able to establish a definitive root cause for the boss fracture. Post repair test vibe readings were just above the 0.6 limit. To reduce the limit as far as possible the following parts were changed: Coupling adaptor. 1-6 axial stages. On the final test run to reduce the vibe readings further the SAG shaft has been rotated 180 degrees out of position.(Engine manufacturer has been consulted and confirm acceptance for the SAG shaft to remain fitted 180 degrees out of position as all vibe readings below 0.6 limit). This producing the lowest vibe readings so far and considered acceptable for return to service. 

Robinson R22: Lycoming O-360: Notthingham/East Midlands - 07/08/2015 (201510787)

Underlying corrosion found on fan wheel assembly.  P/N B174-1 Fanwheel Assy has been removed (405.9hrs) where finish has cracked/flaked. Factory has requested the part be sent back for inspection.

 



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