7-Nov-2012 Source: Eurocopter
On October 22, 2012, during a flight to an offshore platform, a controlled ditching was performed with an EC225 helicopter. No one on board was injured and everyone was brought back to land safely. The helicopter remained afloat thanks to its emergency floatation gear and was recovered by a ship.
An emergency lubrication warning light came on and resulted in the crew making the decision to perform a controlled ditching, as required by the flight manual.
The main gear box has arrived at Eurocopter’s Marignane facility in order to launch a deeper investigation. As already indicated in the AAIB Special Bulletin S6/2012, the initial visual examination has identified a 360° circumferential crack on the bevel gear vertical shaft (which drives the two Main Gear Box (MGB) lubrication pumps), in the vicinity of the weld that joins two sections of the shaft.
Information concerning the ditching of an EC225 on October 22, 2012
Emergency lubrication (EMLUB) system:
This system is installed on the EC225/725 only. The objective of the system is to provide MGB lubrication (with glycol fluid) in the event of a total loss of oil lubrication and in order to provide the crew with additional flight time to perform a safe landing or ditching (without exceeding 30 min of flight).
The initial examinations performed in Eurocopter under the supervision of the AAIB have shown that glycol was found throughout the gearbox casing and on all the gears and bearings of the aircraft that performed the controlled ditching on October 22. There appears to be no visual evidence of heat distress or damage to any of the other components in the MGB, which seems to indicate that the EMLUB system had operated but that a false alarm indicating malfunction had illuminated.
The root cause of the false failure warning has not yet been identified. It has, however, been identified that the maintenance in force needs to be improved. A service bulletin is currently being written to propose a new maintenance procedure associated with specific tools.
Eurocopter is actively participating in the investigation under the AAIB authority and has launched in parallel intensive analyses in order to better understand the root causes of the rupture.
The investigation is conducted by the UK AAIB, which is the only authority allowed to provide official investigations results.
The aim of the protective measures put into place is to reduce the risk of having to perform an emergency ditching in open seas.
EASB 04A009 (EC225); 04A008 (EC725); 01.00.82(AS332); 01.00.47 (AS532) Revision 1 has been approved by EASA and was issued on October 24th.
This EASB is applicable to all aircraft fitted with a new-generation nitrided vertical shaft (identified by part number).
Aircraft equipped with nitrided shafts:
- All EC225/725, as the nitrided shaft is the only design certified for this aircraft type.
- Some AS332/532 are also equipped with nitrided vertical shafts and as a consequence they are also concerned by the limitation
The first-generation carburized vertical shafts are not concerned.
The protective measures, for flights above water beyond safe forced landing distance from land, (typically, flights at a distance from the shore more than 10mn at Vy) consist of:
- A close monitoring of Vibration Health Monitoring (VHM) data without exceeding a defined number of flight hours,
- For aircraft not equipped with VHM, no flights allowed over water beyond safe forced landing distance from land .
The flight hour periodicity has been defined in accordance with the VHM data of the two ditchings (May and October 2012).
Revision 1 of the EASB introduces two changes:
- An enlargement of the batch of nitrided vertical shafts affected by the limitations.
- A decrease of the number of flight hours between two VHM downloads.
The decision was made to enlarge the batch since the second failed shaft was not part of the initial batch of concerned shafts. Currently, all aircraft equipped with nitrided shafts are concerned (even those with a s/n above 5,000).
Based on Eurocopter’s expertise following the analysis of the VHM data of the second controlled ditching, the monitoring interval of the VHM download has been reduced for each helicopter type. It still includes a 50% safety margin.
Reminder: the flight manual (FLM) procedures in the event of an MGB loss of lubrication remain applicable and therefore operators must adapt their flight profile accordingly, also for flights above ground.
Information concerning the first ditching of an EC225 on May 10, 2012
The bevel wheel vertical shaft was found ruptured on the EC225 that performed a controlled ditching in May 2012.
The AAIB issued Special Bulletin S5/2012 on October 17th, 2012. The AAIB report based on tests performed on each part of the emergency lubrication and cooling system as well as inspections of the MGB after ditching confirmed that the system was indeed cooling and lubricating the MGB successfully but that a false alarm of malfunction occurred.
It has been established that all parts of the emergency lubrication system operated within their specifications. During examination, glycol was found throughout the gearbox casing and on all the gears and bearings, which remained in excellent condition.
This evidence indicates that the emergency lubrication system had activated and remained operational for the duration of the flight. Therefore, the warning of system failure indicated to the flight crew was a false alarm and resulted in the crew making the decision to perform an immediate landing, as required by the flight manual.
Eurocopter has already performed various in-flight measurements and is in the process of performing a complete test of the full emergency lubrication system on a test bench with an engine in order to understand the above scenario and define specific corrective actions to be implemented in order to avoid any possible future false alarm of the emergency lubrication system failure.
The men and women of Eurocopter do not make any compromises when it comes to safety. Taking into consideration the concerns of operators, end users, crews and passengers, Eurocopter has mobilized its teams and is devoting all of its efforts in close cooperation with the investigation authorities to fully understand the root cause of the controlled ditchings.