There is some debate at my ATPL school about whether to use 100% of the wind in the CAP Climb Graphs (this is the only graph that doesn't compensate for the head wind / tail wind in the graph).
This is one of the areas that often confuses students: "... should I use the full headwind component or reduce it by 50% before going into the graph"? The CAP 698 itself does not provide much help on clarifying this, aside from a single piece of information listed in the MRJT section above Figure 4.1 (paragraph 1.4 - item f).
My point of view on this issue:
When using the takeoff and landing performance graphs from CAP 698 you have to use the actual reported wind components - i.e. you do not factor in the 50% / 150% rule as it is already incorporated into the graphs. During the aircraft certification process (as per EASA CS-25) the manufacturer has to use the 50/150 wind component values in determining the applicable performance figures. The CS-23/CS-25 documents then also state the Aeroplane Flight Manual (AFM) must include performance data that already include the adjustment by the 50/150 wind component factor.
Excerpts from CS-23 (applicable to SEP+MEP in CAP 698):
AEROPLANE FLIGHT MANUAL
CS 23.1581 - General
(a) An Aeroplane Flight Manual must be submitted to the Agency and it must contain the following:
(1) Information required by CS 23.1583 to 23.1589. [etc ...]
CS 23.1587 - Performance information
(a) For all aeroplanes, the following information must be furnished:
(5) The effect on landing distance of runway slope and 50% of the headwind component and 150% of the tailwind component.
(c) In addition to sub-paragraph (a) and paragraph (b) if appropriate, for normal, utility and aerobatic category aeroplanes, the following information must be furnished:
(3) The effect on take-off distance of runway slope and 50% of the headwind component and 150% of the tailwind component;
Excerpts from CS-25 (applicable to MRJT in CAP 698):
CS 25.105 - Take-off
(d) The take-off data must include, within the established operational limits of the aeroplane, the following operational correction factors:
(1) Not more than 50% of nominal wind components along the take-off path opposite to the direction of take-off, and not less than 150% of nominal wind components along the take-off path in the direction of take-off.
CS 25.125 - Landing
(f) The landing distance data must include correction factors for not more than 50% of the nominal wind components along the landing path opposite to the direction of landing, and not less than 150% of the nominal wind components along the landing path in the direction of landing.
AEROPLANE FLIGHT MANUAL
CS 25.1581 - General
(a) Furnishing information. An aeroplane Flight Manual must be furnished with each aeroplane, and it must contain the following:
(1) Information required by CS 25.1583 to 25.1587. [etc...]
CS 25.1587 - Performance information
(b) Each aeroplane Flight Manual must contain the performance information computed under the applicable provisions of this CS–25 (including CS 25.115, 25.123 and 25.125 for the weights, altitudes, temperatures, wind components, and runway gradients, as applicable) ... [etc...]
AMC 25.1581 - Aeroplane Flight Manual
d) Performance Section
(7) Take-off and Accelerate-Stop Distances. Take-off and accelerate-stop distances, complying with CS 25.105, 25.109, 25.113, and 25.1591 must be provided ... [etc...]
The feedback from past students is that they got questions wrong in the EASA exams by using 100% of the wind. ie not using "150% of the tailwind/ 50% of the headwind " rule.
EASA has admitted to having errors in their question bank (see excerpt from minutes of EASA consultative body meeting below). Their estimate is that between 10-20% of the ECQB questions / answers contain some errors or inaccuracies. If you encounter a performance question on your EASA exam (relating to a CAP 698 graph) and your answer gets marked as wrong because you did not apply the 50/150 wind component factor, I would definitely recommend to appeal the question.
European Aviation Safety Agency
MINUTES OF MEETING
Subject: AGNA Meeting 01-2011
Date: 22-23 March 2011
...
Point 5 on the meeting agenda:
...
► New issue: Central Question Bank (CQB)
...
► AUSTRIA pointed out that some Member States have corrected mistakes of the JAA database (wrong questions, wrong answers, etc ensuring a correct application of the JAA database – which was agreed to be the only one used). Agency was not aware of this as the JAA database was agreed to be the only one to be used. Target should be to eliminate the mistakes present in the current questions and to review the process.
► SWEDEN asked what the timeframe is concerning the review of questions of the existing CQB? Agency replied that the future group together with the Agency will try to identify erroneous questions. The number of wrong questions is not known but Member States indicated that may be 10-20% of questions are not correct in the existing database. For this task the Agency needs help of NAA experts. ... [etc...]