MRJT Flight Planning question.

[coolcaptain]

With regards to CAP697, MRJT 1, Figure 4.3.1a

(or any of the "simplified flight planning" charts)


When you start out at the bottom, with the "Trip Distance, Nautical Ground Miles" you then have the option to include a mean head/tailwind for the trip.

The example trip is 350nm, with a 50kt headwind.

Why then, would the line go straight up to the REF line, and *then* follow the curve. What if you had an 80kt tailwind, or a 30kt tailwind... ?? Surely you wouldn't just go straight up... perhaps tailwinds don't count? I'm baffled.

[RichardH]

As with all graphs going through in the "normal" method, you should always go to the reference line first then follow then trade or guide lines.

So in the case of headwind go to reference line first then follow the trade line up to your headwind component, then continue to calculate fuel based upon cruise level and landing weight.

In the case of a tailwind, again reference line first then follow the trade line DOWN before going up to cruise level and landing weight for fuel.

Logically thinking about a problem a headwind is going to increase your time and FUEL and tailwind in going to reduce your time and FUEL.

Give yourself an example with the same parameters, but use a 100 kt tailwind and 100 kt headwind, you shall find a big difference.

[coolcaptain]

Richard,


Thanks for the reply. I realize my thinking was illogical but for some reason couldn't wrap my brain around it. I never thought to go back from the ref line for a tailwind, makes alot of sense now thanks again.

[TenAndie]

In the exam they may ask you to do one backwards. Now that is when it gets complicated !!!!

[Send Clowns]

Someone who set those graphs was dumb as a mule. Why they didn't just adjust the scale and have the reference line as the first line I don't know.

Rule is: working the 'normal' way follow straight to the reference line then follow guidelines to the piece of data you are incorporating, even if that means going back on yourself, before continuing straight. If using the graph in a 'reverse' sense, follow straight to the graph-paper line representing the piece of data you are incorporating, then follow the guidelines to the reference line!

Hope that helps a little!

Send Clowns
Flight Planning, BCFT

[Devils Itch]

Sends clowns.

I dont see how you could redesign the graph to make it easier to read. As i recall, the graphs take into account the fact that the legal requirements state that you need to take 50% of the head wind and 150% of a tail wind when doing performance calculations, thus the contour lines will have very different gradients....which they do. Now if we put the reference line at the start, both the tail and headwind components would be above the reference line going in different directions. This , in my opinion, would clutter the graph even more. Thus making the already questionable print quality of the manuals that you receive in the exams, even harder to use when under exam stress.

Do you know the person who put the manuals together? I heard he received approximately £60k for his efforts. To me it looks like all he did was photocopy the boieng manual. Not a bad job if you can get it!