Safety Alert Says High Manifold Pressures can "Substantially Reduce" Blade Life; Alert Prompted by Blade Separation.

by ANN Senior Correspondent Kevin R.C. "Hognose" O'Brien

Mechanical failure is every rotorcraft pilot's nightmare, and pilot training stresses the importance of following procedures and respecting limits. Robinson Helicopter Company recently responded to a main rotor blade failure with a warning to all R-22 operators. "Exceeding Manifold Pressure Limits Can Cause Blade Failure," was the title, and the essence, of Robinson's R-22 Safety Alert. Robinson makes three points (and I quote):

"1. If the helicopter has been occasionally operated above manifold pressure limits, replace main rotor blades.
2. If the helicopter is normally parked outside in humid climates, particularly in tropical or coastal areas, replace A016-2 main rotor blades prior to 5 years time in service due to possible internal corrosion.
3. If main rotor vibration increases during flight, make an immediate safe landing and determine the cause of vibration before further flight. If cause cannot be determined, replace main rotor blades before further flight."

The A016-2 rotor blades have tip weights and a ten calendar year service life. Unweighted blades (Part A016-1) should have been removed from service already. The current part (A016-4) has a twelve year, 2200-hour service life and stainless steel skins, which should help prevent the corrosion that has led to an emergency AD (2004-06-52) this year as well as several factory safety and service messages.

Robinson also advises operators to review Safety Notices 37 and 39. Notice 37, issued in December 2001, is particularly appropriate: "EXCEEDING APPROVED LIMITATIONS CAN BE FATAL" it warns in capital letters, and explains why even a brief flight above airspeed or manifold pressure limits can lead to mortal consequences. Notice 39, from , "A catastrophic rotor blade fatigue failure can be averted if pilots and mechanics are alert....If main rotor vibration rapidly increases or becomes severe during flight, make an immediate safe landing. Do not attempt to continue flight to a convenient destination." Several blade failures have been preceded by a notable increase in vibration and Robbie operators should not delay landing if they get this warning.

In addition, R-22 operators & maintenance stations would be well advised to review Service Letter 54 on the subject of rotor life, which was revised this summer. It also was written in response to rotor blade failure mishaps (like a July 28th incident where the pilot apparently didn't understand the severity of the problem, didn't land immediately and didn't make it) and explains the differences between R-22 blade part numbers, causes of and preventive measures for blade failure, how to comply with AD 2004-06-52, and how to order replacement blades.

It is all but tautological to say that exceeding limits can cause failure (that's why they're "limits," not "suggestions"), but Robinson felt the need to issue this alert after a blade failure at 700 hours. They appear to be referring to a near-accident in Britain last month. The accident remains under investigation by the British AAIB, but apparently, "the pilot noticed a vibration after transitioning to a hover." The machine was set down safely -- in compliance with the warning in Safety Notice 39 -- but, "post flight inspection of the main rotor system revealed that a main rotor blade exhibited a crack, which extended chordwise from the trailing edge, through 75 percent of the chord. In addition, the teeter head was extremely stiff." No word on how long the pilot shook like a leaf after seeing that. The good news is that nobody was hurt.

The safety alert is available in the support section of the Robinson Helicopter Company website. It has also been disseminated by HAI and other helicopter forums. This Safety Alert is unlikely to be popular with operators, particularly the 5 year limit on outdoor-parked pre-stainless R-22 rotor blades, but losing a rotor blade is not popular with anybody, so it's hard to argue Robinson's point. If your life is not worth the $15,000 to $25,000 cost of new blades (costs are detailed in Service Letter 54) you probably shouldn't be operating rotorcraft.

The R-22, which first flew in 1975, and was certfied in 1979, is an extremely popular 2-seat sport, utility and training helicopter, with well over 3,000 delivered. Its low-inertia rotor system gives it lively flying characteristics that make it ideal for such purposes. Robinson is also unusual in the industry in having a single fixed overhaul life for the entire airframe. This helps keep serviceability under the eye of the factory, while giving operators "known quantities" with respect to factory-remanufacture schedules and costs.

FMI: www.robinsonheli.com