New Airworthiness Directive
on Cessna Caravan Vindicates
The Wolk Law Firm's Warnings
on Known Icing
In a stunning reversal the Federal Aviation Administration has
issued AD 2007-10-15 on the Cessna Caravan.
Icing wind tunnel research
commissioned by The Wolk Law Firm in connection with the case of Randolph vs.Cessna revealed serious flaws in the design and operation of the deicing
system of that aircraft. Experts hired by Arthur Alan Wolk confirmed that the problems ranged from the choice of wing airfoil,
design of the deicing boots, flaws in the design of the inflation hardware, inadequate stall warning, underpowered engine,
and complete inadequacy of the pilot's operating handbook for safe flight into known icing conditions.
After a spate of icing accidents Cessna Aircraft Company, encouraged by the FAA and the NTSB revised
the Pilot's Operating Handbook to prohibit the use of flaps when airspeed reductions occurred due to unshed ice accumulations.
One of the experts working for The Wolk Law Firm, Harry Riblet, a noted designer of general aviation
airfoils openly criticized the Cessna, FAA, and NTSB action and wrote to them repeatedly warning that use of the flaps could
help but not cure the controllability problems with the airplane when flying in icing conditions. Riblet was ridiculed by
the Government and Cessna even though his airfoils adopted for use by homebuilders around the world had proven themselves
stall spin proof.
This Airworthiness Directive, with the full force and effect
of law, now removes any restriction for the use of flaps in icing conditions and instead requires their use when the aircraft
airspeed is reduced to 110 knots or less.
It also prohibits the flight of the
aircraft in moderate icing conditions for which the aircraft was originally certificated and removes the words "certified
for flight into known icing conditions" from the handbook without revoking the certification entirely.
The AD requires installation of a low speed warning in all Cessna Caravans and cautions pilots that
the stall warning may be completely unreliable in icing conditions.
What is remarkable
about the Airworthiness Directive is what it doesn't do.
1. It does not revoke
the "known icing certification" of the Caravan which means it may still be dispatched into conditions where ice
is reported or forecast.
2. It ignores the fact that moderate icing is unpredictable
so it may still not be possible for pilots to safely exit those conditions.
3.
It ignores the bad design of the deicing boots and does not require the introduction of a water separator into the system
to prevent ice boot inflation line icing.
4. It does not require that all Caravan
pilots be taught how to recognize and recover from a tail stall.
5. It does not
require the installation of vortex generators on the boots of the wing and the horizontal stabilizer to delay the onset of
ice induced stall.
6. It does not require Cessna to install a stall warning indicator
that is impervious to ice induced errors.
7. It defines moderate icing encounters
as a reduction in airspeed to 120 knots in cruise flight which is already in most instances a state beyond which the aircraft
will be recoverable once control is lost.
8. It further defines moderate icing
as an accumulation of 1/4 inch on the wing strut which is the amount of ice accumulation Cessna requires before operation
of the deicing boots in the first place even in light icing conditions.
What this
AD demonstrates once again is the FAA does not understand yet the aerodynamics of the Cessna Caravan but had to do something
to stem the constant series of ice related accidents with these aircraft.
Instead
of doing what's right and what's needed, it granted Cessna yet another reprieve at the expense of safety. More will die or
be maimed next winter but hopefully this is a start to the end of this battle.
Arthur
Alan Wolk
June 2007
