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requirements but is not considered to be a limiting value for aircraft handling
characteristics. This "demonstrated" value should be included as information in the
Aircraft Flight Manual.
• A crosswind component value may be established which is considered to be a maximum
limiting value up to which it is safe to operate for takeoff and landing. This "limiting"
value should be shown in the Operating Limitations section of the AFM.
Procedures.
(i) Configuration. These tests should be conducted in the following configurations:
• At light weight and aft CG (this is desirable; however, flexibility should be permitted).
• Normal takeoff and landing flap configurations using the recommended procedures.
• Normal usage of thrust reversers. Particular attention should be paid to any degradation
of rudder effectiveness due to thrust reverser airflow effects.
• Yaw dampers/turn co-ordinator On, or Off, whichever is applicable.
(ii) Test Procedure and Required Data. Three takeoffs and three landings, with at least one
landing to a full stop, should be conducted in a 90-degree crosswind component of at least 20
knots or 0.2 VS0, whichever is greater, except that it need not exceed 25 knots. For each test
condition, a qualitative evaluation by the pilot of aircraft control capability, forces, aircraft
dynamic reaction in gusty crosswinds (if available), and general handling characteristics should
be conducted. The aircraft must be satisfactorily controllable without requiring exceptional
piloting skill or strength. Wind data from the INS systems, tower, or portable ground recording
stations should be corrected to a 90-degree crosswind component and to a height of 10 meters.
These guidelines give a lot more information than the rules themselves. However, these
guidelines still leave plenty of room for different interpretations by its users. Let us have a
closer look at what the text in the Flight Test Guide really means for crosswind certification. A
distinction is made between manual landings and autolands.
NLR-TP-2006-324
9
3 Manual landing
According to the Flight Test Guide there are two possibilities on how to note crosswinds in the
Aircraft Flight Manual AFM.1 If the demonstrated crosswind is not considered to be a limiting
value for aircraft handling characteristics, this demonstrated value can be placed as information
in the AFM. Higher crosswinds are then allowed when the applicable operational requirements
and the airline specification allow it. For instance, the AFM of the B737-400 states the
following on crosswind “The maximum demonstrated crosswind component for takeoff and
landing is 35 knots reported wind at 10 meter height. This component is not considered to be
limiting on a dry runway with all engines operating”. Does this mean that there is no limit for
this aircraft? The simple answer is NO, this aircraft will have a limit but it was not found during
certification. Other manufacturers make very similar statements for their aircraft. Interesting is
the fact that nothing is said about gusts. It remains unclear whether in the example of the B737-
400 the crosswind of 35 knots includes or excludes gusts. This fact is important when the
operator is using the demonstrated crosswind in their Aircraft Operating Manual AOM. Up to
this moment only Airbus gives a gust value in the certified crosswind. An overview of
maximum demonstrated crosswinds of a number of aircraft is shown in Figure 1. It is clear from
this figure that the demonstrated crosswind capabilities have not shown a significant trend
during the last forty years of aircraft certification. The average demonstrated crosswind is 30
knots. Amongst the different aircraft significant variation in the demonstrated crosswinds exists.
One of the reasons of this variation is due to Mother Nature. An aircraft manufacturer has no
influence on the weather. In a certification flight test program of new aircraft, every test is
carefully planned and scheduled. For crosswind certification a location and week are selected
for which it is most likely to have strong wind conditions. When the moment of truth is there the
actual wind maybe far less than hoped for. Usually there is no time available up to the
certification date of the aircraft to conduct additional crosswind test flights. It is not uncommon
that after the aircraft was certified additional test flights are made by the manufacturer to
demonstrate higher crosswind capabilities.
1 Most operators do not use the AFM as an operational manual, but are authorised to use the Aircraft Operations Manual (AOM)
as a substitute for the AFM instead. The information in the AOM is based on and in agreement with limitations in the AFM. With
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