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crosswind limitation was 20 knots, but the first officer stated that the limitation was 25 knots. In
the testimony at the National Transportation Safety Board's public hearing on this accident, the
first officer stated that neither he nor the captain checked the actual crosswind limitation in the
flight manual. The first officer testified that he had taken the manual out but that the captain had
signalled him to put the manual away because the captain was confident that the crosswind
limitation was 20 knots. During the accident investigation, it was determined that the Flight
Manual crosswind limit was actually 10 knots, considering the wet runway and the fact that the
RVR as less than 1800 ft. After touchdown directional control was lost due a combination of
high crosswind, wet runway, and use of reverse thrust greater than 1.3 engine pressure ratio,
which decreased the rudder effectiveness on this aircraft type.
The Safety Board determined that contributing to the accident was, amongst others, the flight
crew’s continuation of the approach to a landing when the company’s maximum crosswind
component was exceeded.
The above accident is an illustration of an event in which crosswind limits were exceeded with
serious consequences. Many pilots will have encountered the situation in which the actual
crosswind conditions at a destination were close to the company’s limits. Not many pilots are
actually aware of how crosswind limits are determined for an aircraft. This article will discuss
the crosswind certification process and how it is translated to the normal day-to-day flight
operation.
NLR-TP-2006-324
7
2 Crosswind Certification Process
Aircraft with a maximum takeoff mass of 5,700 kg or higher are certified according to the US
Federal Aviation Regulation FAR 25 and the European equivalent JAR/CS 25. Both JAR/CS 25
as FAR 25 state the following regarding crosswind:
§25.233 Directional stability and control.
(a) There may be no uncontrollable ground-looping tendency in 90-degree crosswinds, up to a
wind velocity of 20 knots or 0.2 VS0, whichever is greater, except that the wind velocity need not
exceed 25 knots at any speed at which the aircraft may be expected to be operated on the ground.
This may be shown while establishing the 90-degree cross component of wind velocity required
by §25.237.
(b) Landplanes must be satisfactorily controllable, without exceptional piloting skill or alertness,
in power-off landings at normal landing speed, without using brakes or engine power to maintain
a straight path. This may be shown during power-off landings made in conjunction with other
tests.
§25.237 Wind velocities.
For landplanes and amphibians, a 90-degree cross component of wind velocity, demonstrated to
be safe for takeoff and landing, must be established for dry runways and must be at least 20 knots
or 0.2 VS0, whichever is greater, except that it need not exceed 25 knots.
Note that VSO means the stall speed or the minimum steady flight speed in the landing
configuration. The wind velocity must be measured at a height of 10 meters above the surface, or
corrected for the difference between the height at which the wind velocity is measured and the 10-
meter height.
When these rules are carefully examined, the following can be noticed:
• Only dry runways have to be considered,
• It is not clear if the wind velocity includes gusts or not,
• No crosswind limits have to be established, only demonstrated values.
Like with almost any rule given in JAR/CS/FAR 25 the aircraft manufacturer needs additional
guidelines to actual know how the comply to these rules. The FAA has published a flight test
guide for the certification of transport category aircraft in the form of an Advisory Circular (AC
25-7A) known as the Flight Test Guide. This Advisory Circular contains guidelines about the
crosswind demonstration flight tests. The important parts of the FAA Flight Test Guide are as
follows.
NLR-TP-2006-324
8
25.237 - Wind Velocities.
Explanation.
• There must be a 90-degree crosswind component established that is shown to be safe for
takeoff and landing on dry runways.
• The aircraft must exhibit satisfactory controllability and handling characteristics in 90-
degree crosswinds at any ground speed at which the aircraft is expected to operate.
Crosswind Demonstration.
A 90-degree crosswind component at 10 meters of at least 20 knots or 0.2 VS0, whichever is
greater, except that it need not exceed 25 knots, must be demonstrated during type certification
tests.
There are two results possible:
• A crosswind component value may be established which meets the minimum
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