EC225 LP Super Puma Helicopter May Have A Gearbox Shaft Problem

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EC225 LP Super Puma Helicopter May Have A Gearbox Shaft Problem

By Daniel Baxter

October 28, 2012 - The United Kingdom Air Accidents Investigation Branch (AAIB) has published a Special Bulletin on the S6/2012 - EC225 LP Super Puma, G-CHCN helicopter, the bulletin appears to make a link between the incident that occurred on October 22, and an incident in May. The root problems appear once again to be with the gearbox shaft and the emergency lubrication system.

There is now growing concerns amongst pilots of the safety of this helicopter, The British Airline Pilots Association (BALPA) has questioned what EASA and Eurocopter have done to ensure that the fault identified in May’s incident has been rectified on all helicopters of this type. Whatever action has been put in place has clearly not been sufficient if the AAIB’s initial investigation proves to be correct.

For instance, it appears that the vertical shaft in this helicopter was not one of those identified by Eurocopter has one needing special attention. BALPA is calling for EASA to be transparent about its actions to date. Safety experts are currently looking at the issue in detail and BALPA intend to keep their members who fly this helicopter up to date with their views over the safety of this type of aircraft.

On October 22, 2012 the crew of the EC225 LP Super Puma, G-CHCN helicopter carried out a controlled ditching following indications of a failure of the main gearbox (MGB) lubrication system and, subsequently, a warning indicating failure of the emergency lubrication system. All passengers and crew evacuated the helicopter and were subsequently rescued without injury.

The aircraft was on a planned flight from Aberdeen International Airport to the West Phoenix drilling rig, approximately 226 nm to the north in the North Sea, approximately 32 NM southwest of Sumburgh, Shetland Islands in Scotland. The crew reported that, while in cruise flight 140 kt and 3,000 ft with approximately 81% total torque applied, the XMSN (transmission) caption illuminated on the Central Warning Panel (CWP).

They added that the M.P (main pressure), MGB.T (main gearbox oil temperature) and the S/B.P (standby oil pump pressure) captions on the Vehicle Management System (VMS) also illuminated and the main gearbox oil pressure indicated zero. The MGB.P (main gear box oil pressure) caption then illuminated on the CWP. The crew actioned the ‘Total Loss of MGB (Main Gear Box)Oil Pressure’ checklist, which required the activation of the MGB emergency lubrication system (EMLUB).

However, within a minute the MGB EMLUB caption illuminated on the CWP indicating that the emergency lubrication system had failed. As a result of the MGB EMLUB caption illuminating, the crew carried out the ‘Emergency Landing – Power ON’ checklist and successfully ditched the helicopter in the sea, close to a ship. The passengers and crew evacuated the helicopter and boarded two life rafts before being rescued and transported to the ship. There were no reported injuries.

The helicopter has been recovered from the sea and transported to Aberdeen for examination. The Digital Voice and Data Recorder (DVDR) and other items of avionics had been removed and transported to Farnborough for analysis. The AAIB dispatched a team of investigators and support staff to Aberdeen.

The main gearbox lubrication system includes two mechanically-driven oil pumps and a crew-activated emergency lubrication system. The gearbox normally contains 22 litres of oil. The oil pumps (a main pump and a standby pump) are driven by the oil pump drive pinion located on the lower part of the bevel gear vertical shaft within the main gearbox. Vertical shafts of this type are fitted to all EC225 and some AS332 L1 and L2 helicopters. The bevel gear vertical shaft is manufactured from two sections welded together. The emergency lubrication system includes an 11 litre tank, containing a mixture of glycol and water (Hydrosafe 620), and an electric pump. When activated, Hydrosafe 620 is pumped into a distributor, mixed with engine bleed air, and sprayed into the main gearbox. The spray is designed to provide a minimum of 30 minutes of main gearbox cooling and lubrication in the event of total loss of oil lubrication. The MGB EMLUB caption illuminates if the system fails.

Vibration data prior to the accident flight was examined and the vibration signatures known as the MOD 45 indicator, which monitors the meshing frequency of the bevel gear and the MOD 70 indicator, which monitors the meshing frequency of the oil pump wheels, show some exceedances. These two indicators each have two alert thresholds; a lower threshold designated AMBER, and a higher threshold designated RED.

During the first two sectors, on Monday 22 October, the helicopter flew for approximately 3 hours 50 minutes. During the first sector, the MOD 45 indicator showed an increasing trend that then exceeded the AMBER trigger threshold followed, later during that sector, by an exceedance of the RED threshold. During the second sector three further data points were recorded, all above the RED threshold and increasing in magnitude. The MOD 70 data showed one exceedance; a value in excess of the RED threshold which occurred during the second sector at the same time as the final MOD 45 point. Indicators Kg and Kr, which are also associated with the bevel shaft and wheels, also showed increasing trends and exceeded their AMBER thresholds.

Preliminary engineering investigation - the main gearbox was drained. An initial visual examination has identified a 360 degree circumferential crack on the bevel gear vertical shaft, in the vicinity of the weld that joins two sections of the shaft. Therefore, the main and standby oil pump gears were no longer being driven.

Related incident - On May 10, 2012 there was an accident to an EC225 LP (G-REDW) in which the bevel gear vertical shaft failed. That investigation is ongoing and the manufacturer issued a Service Bulletin, which was subsequently mandated by Airworthiness Directive (AD 2012-0115E) and contained requirements applicable to EC 225 LP.