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In summary, the Flight Test Guide leaves plenty of room for significant variations in the derived
crosswind capabilities of an aircraft. The Flight Test Guide is still much under development.
The latest draft of the revised Flight Test Guide (dated February 2002) gives some more
clarification on certain points regarding crosswind certification, however the comments made
here still apply.
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4 Autoland
Many modern jet transport aircraft are certified and capable of performing autoland operations.
These autolands are constrained with respect to crosswind. As opposed to the demonstrated
crosswinds for manual landings, the autoland crosswind is always a limit. Autoland certification
under crosswind conditions is established primarily through a large number of computer
simulations of automatic landings of that particular aircraft. The simulations must show that
under varying conditions the touch down performance complies with the criteria set by the
FAR/JAR autoland requirements. By means of a specific set of flight tests, it must be
demonstrated that the actual touch down performance falls within the footprint of the performed
simulations. The maximum crosswind values for autoland operations are often less than the
manually demonstrated crosswind landings. This is sometimes caused by system constraints.
However, autoland certification is a time consuming process and therefore costly. Since
autoland capabilities are mainly intended for low visibility operations (CATIII), the need for
high crosswind limits is simply not there. This is the main reason for the lower crosswind limits.
Many autoland systems should be able to handle higher crosswinds. For instance, the B767-400
has a maximum certified crosswind during autoland of 25 knots. Flight test with this aircraft
showed that autolands in a 40 knots crosswind could be made. Similar the Fokker 100 has a
limit of 25 knots, however flight tests showed that this aircraft could handle crosswinds up to 38
knots including gusts during an autoland.
5 Use of crosswind limits in practice
In the previous section it is explained how your aircraft has been certified for crosswind
operations. The question remains how all this is translated into the numbers that you can find in
your AOM. First of all, if hard crosswind limits have been established for an aircraft the AOM
may never show higher values. However, as already noted most aircraft do not have hard
crosswind limits. So, what happens then? A survey was taken of a number of operators
worldwide. These operators were requested to send the crosswind limits for the aircraft they
operated as published in their AOMs. The operators were also asked to provide information
about any additional limitation posed on crosswind operations. From this survey the following
interesting facts are identified for the operators surveyed:
• Most operators use crosswind limits that do not exceed the demonstrated crosswinds,
• Most of the operators include gusts in their crosswind limits,
• All operators adjust the crosswind limits for wet and contaminated runways,
• Some of the operators adjust the crosswind limits for visibility,
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• Most of the operators have reduced crosswind limits for less experienced pilots. (Note that
for instance FAR part 121.438 demands that first officers that have less than 100 hrs
currency on type, are not allowed to make crosswind landings in excess of 15 knots),
• Most operators account for runway width.
Interesting is the fact that there are operators that use crosswind limits that exceed the
demonstrated values. This is no problem as long as the aircraft does not have hard limits, at least
seen from a legal point of view. Boeing has derived crosswind guidelines that exceed the
demonstrated values, through piloted evaluations in an engineering simulator and engineering
judgement without a having conducted a single flight test. These evaluations were made upon
the request of some ETOPS operators who wanted to have more operational flexibility
regarding the availability of alternate airports during an ETOPS flight. There has been criticism
on this approach by certification authorities. Remarkable is the fact that these crosswind
guidelines are based on steady wind (no gusts) conditions due to the difficulty in modelling gust
in the flight simulator. However the acceptable gust value is still left to the operator. Interesting
are the conclusions made by the Irish accident investigation board regarding a crosswind related
accident with a B737-800: “Lower crosswind limits aid the crews decision making process…in
interests of flight safety” and “…it would seem prudent for the operator to review their
　
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