Unlike its sister ship the EC225, the EC175’s main gearbox has no backup lubrication system, which could present a problem should it experience a total loss of oil. To compensate for this, its components have been designed to withstand the absence of lubricant for a limited period of time. Airbus Helicopters so far has certified a 15-minute dry-run capability (which involved a 30-minute demonstration). Further tests are scheduled for 2015 in a bid to increase the certified duration to at least 30 minutes.
The emergency lubrication system of the EC225 was modified last summer. EASA approved the changes, including replacing the air and glycol pressure switches, modifying the glycol pump and improving the system’s maintenance. The modification eliminates false alarms and cancels flight manual limitations. In other words, a crew can count on a 30-minute lubrication backup in the event of total loss of oil.
The modification approval went relatively unnoticed last year, as the focus last summer was on the shaft itself.
The National Institute for Aviation Research (NIAR) at Wichita State University is offering a new oil analysis service for all types of piston and turbine engines. NIAR’s new oil analysis lab can perform trivector analysis (wear, contamination, general oil chemistry); infrared spectroscopy (monitors molecular substance in oil); particle count/shape recognition; elemental analysis (checking for elements that correlate to contaminants, wear metals and additives); and viscosity testing.
Loss of lubrication to the main gearbox (MGB) has been responsible for several crashes, ditchings and precautionary landings in large transport category helicopters in recent years. These accidents set off broad debate as to exactly what is required of main gearboxes under Part 29 certification of the U.S.
The EASA has issued a new emergency AD on the Eurocopter EC225, requiring crews to land or ditch immediately if the main gearbox’s back-up lubrication system activates. “Investigations on the [emergency lubrication] system have revealed an area of the flight envelope in which the [system’s] performance is different from that assumed during certification,” the EASA said. The system was designed to allow for 30 minutes of flight after loss of oil lubrication.
The UK Air Accidents Investigation Branch (AAIB) has explained why the emergency lubrication system sent a “failure” warning–while working nominally–to the crews of the two Eurocopter EC225s that ditched in the North Sea last year.
The FAA is moving to redefine what “extremely remote” means when it comes to Part 29 certification provisions regarding loss of helicopter gearbox lubrication. The S-92 originally gained certification after Sikorsky convinced the FAA that complete loss of lubrication was extremely remote. Failure of the main rotor gearbox lubrication system is blamed for the fatal ditching of a Cougar Helicopters S-92A off Newfoundland in March 2009.