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I've got my 41CV up and running again. Have ROMS for Aviation, Math Functions, Time Functions and X Functions installed.

I'm firming up some ideas on a In-Flight Planning program, to solve for what we call Critical Point (or Equal Time Point) and Last Point of Safe Diversion calculations.

A critical point is a point along a flight planned route at which it will be quicker to proceed to a destination (or off-track alternate) than to return to base.

A Last Point of Safe Diversion ('point of no return') is a fuel flow v fuel qty available problem. How far can I proceed from my point of departure toward my destination and still return home or to another airport with legal reserves intact.

Both CP's and LPOSD are affected by wind - they 'move into wind.' Also the reason I may be asking the question is if I have an emergency - if one engine fails or the cabin depressurises, I will be proceeding slower, at a different fuel burn rate, at a lower level in possibly different winds.

I think that the place to start is to use addition of vectors - wind at a particular level is a vector, and a flight plan is a speed in a direction for a given distance at a more or less constant fuel flow, over a defined time period.

Inputs would be the aircraft magnetic track,true airspeed and fuel burn rate at the normal cruising level, true airspeed and fuel burn rate at the abnormal operating level, the distance to the destination, the wind direction and velocity at both levels, plus the magnetic bearing and distance to a possible alternate airport. For LPOSD calcs, would also need to input the flight fuel available (fuel less reserves)

Any body brave enough to predict whether vector addition is the way to go?

Hows that for a big first question on the forum?!!

Nick,

I use my HP-41 to assist with my flying. The problem you are discussing is the "Wind Triangle" problem, and the Aviation module has a solution within the Flight Plan program. I did not like the program, so derived my own program instead. This problem is most commonly solved using one of the "triangle" solutions (SSA), several calculating references exist (HP-41 Math Module, TI-58/59 Master Module). I don't think that it is possible to solve the problem with vector addition, since you don't know enough about the vectors. You know the wind vector (both angle and length), you know the magnetic course (angle) but not length (ground speed) of the ground motion vector, and you know the True Air Speed (length), but not magnetic heading (angle) of the apparent motion vector. Therefore the triangle solution (side-side-angle) must be used.