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  1. #1
    Wannabe Pilot southern_flyer's Avatar
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    Why are my estimated times during planning vastly different to reality?

    Hi - a recurring theme for me and I'm at a bit of a loss to find the answer.

    Whenever I plan a flight, I think that I do everything right: I look at the forecast wind (at height), calculate my distances correctly, adjust for wind direction and velocity, factor in 'faffing', adjust for TAS and so forth...and I end up with a nice plan for my flight.

    But when I actually fly it, the flights always take much much much longer than I've estimated. This is both out and back - so it's not necessarily a wind thing.

    A great example is that I had my first solo QXC today: Deanland to Goodwood, routing overhead Shoreham: 35 nautical miles.

    At 75kts, Sky Demon suggests it's a 27 minute flight. My own planning - with plenty of rounding and contingency - made it 39 minutes. But when I landed and checked, it was 55 minutes from take-off to landing. The return journey was 50 minutes. We're talking nearly double what Sky Demon thinks it should be.

    It's the same with any flight I plan - and I can't seem to work out what I'm doing wrong. Or - perhaps I'm not doing anything 'wrong', but the little twists and dips and kinks in the flight (given that no-one flies perfectly straight) add up. In which case, how should I accommodate this in my planning.

    I'm certain I'm not doing any calculations wrong, nor am I getting caught up by the wind (as flights are never shorted in time than I projected) - but something's going wrong. Every flight I plan ends up taking at least 50% longer than the planning stage suggests.

    Any ideas?


  2. #2
    Co-Pilot Martin Watson's Avatar
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    I don't know what you mean by faffing, rounding and contingency. What are they for?
    Unless you are wandering about all over the sky your flight times from overhead one turn point to the next will be accurate to the minute. Dead reckoning really is that accurate. I can only think of two possible explanations
    1. The wind aloft is very different to what you used when planning (perfectly possible and your instructor should show you how to check once in the air if it's different)
    2. You are simply confusing overall flight time with time taken to fly cross country - the time positioning to join the circuit at your destination and the time in the circuit are surprisingly long.
    HTH
    Martin
    BMAA 5370
    Fixed wing instruction, examinations and revalidations in Norfolk.


  3. #3
    Captain MadamBreakneck's Avatar
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    I agree with Martin. Additionally, TAS adjustments at our heights and speeds will be less than any ASI error. Your calculation will be overhead to overhead, so in overall time you'll need more. How much more will depend on what you are counting, eg taxi time, engine warm-up time, etc. Even if you time take-off to landing you'll be needing to add time in circuit and such - is this what you mean by 'faffing'?

    For the dead reckoning portion of the flight, I used to get my students to select a visual reference point en route and out of the circuit that they could get to easily by simple local area piloting. Ditto at the other end; plan an obvious reference point which will allow you to position for the airfield join (f'rinstance, On the Goodwod flight having followed the A27 from Shoreham, you could consider using the Fontwell Park racecourse which is about 4 miles away). Once you got there you'll be flying visually to wherever you need to be to join the circuit - which takes as long as it takes.

    Obviously you will have planned to have enough fuel on board for the extra time, and a go-around (or three) and a diversion, not just the dead reckoning phase of the flight.



    Back to just bimbling in the TST.

    No longer instructing - just pontificating..
    and now a Tai Chi instructor


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