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.