Winds Aloft Calculation

A commenter on a post regarding the PPL tests had trouble with the following question:

The average wind applicable to a direct flight from Winnipeg (CYWG) to Brandon (CYBR) at 5,500 ft would be
(1) 290°M at 30 kt.
(2) 290°T at 30 kt.
(3) 310°M at 31 kt.
(4) 310°T at 31 kt.

FDCN CWAO 061920
ISSUED 1200Z 07 FEB 2007 FOR USE 6-17Z

  3000 6000 9000 12000 18000 24000
YWG 2825 2728-07 2932-10 2935-15 2939-26 2841-38
YBR 3030 3132-06 3133-10 3135-15 3041-28 2948-40
YYQ 3529 3428-13 3229-14 3130-19 3032-32 2733-42
YYL 3327 3435-10 3338-14 3337-19 3136-31 3038-44

He got as far as interpolating the wind speeds and directions at 4,500 feet by averaging the respective values but did not know how to proceed after that. Here is how I solved it:

The pertinent information is as follows:

  3000 6000
YWG 2825 2728-07
YBR 3030 3132-06

Between 6,000’ and 3,000’ there is a difference of 3,000’. The altitude required is 5,500’ which is 2,500’ above 3,000’ (or 500’ below 6,000’ depending how you look at it. For the purposes of this example I will be using the 2,500’). There are two steps to this problem:

  1. Find wind speed and direction at the required altitude at the respective airports.
  2. Average them to find the the average wind.

Step 1: Finding wind speed and direction at the respective airports

I will show you the calculation for YWG. Follow the same steps to find the values at YBR.

Wind Direction Adjustment = (270 – 280) * 2500 / 3000 = – 8.333…
Wind Speed Adjustment = (28 – 25) * 2500 / 3000 = 2.5

Wind Direction = 280 + –8.333… = 271°
Wind Speed = 25 + 2.5 = 27.5 kt

At YBR the wind direction would be 308° and wind speed would be 32 kt.

Explanation: Finding the wind at non-reported levels is simply a matter of properly interpolating the information you are provided. In this case I used a weighted average to give me the values I needed. One thing to keep in mind with this calculation is that order is important. The order I followed was going from 6,000’ (I took the values here) to 3,000’ (subtracted these values) then back up to 5,500’ (multiplied by the weight, 2,500/3,000 and added to the values at 3,000’).

Image showing the order of calculation: First find the difference between the values at the different

Another way to think about it is you will be going 2,500 / 3,000 = 83% of the way from 3,000’ to 6,000’ so you add 83% of the difference between measurements at the different altitudes to the values at the lower altitude (or you subtract 17% of the difference from the values at the higher altitude).

Step 2: Average wind

Average wind direction = (308 + 271) / 2 = 289.5
Average wind speed = (32 + 27.5) / 2 = 29.75

With rounding, the applicable wind is from 290 at 30 kts. Keeping in mind that the FD reports directions in degrees TRUE leads to the correct answer being (2) 290°T at 30 kt.

Notice that these calculations assume the change from one altitude to another is linear which may not always be the case.

How would you have solved it? Leave your reply in the comments!

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Confusion in the cockpit

I would like to share with you two recent situations I found myself in while flying around to illustrate the fact that, as a pilot, you can’t let your mind wander even for a minute.

 Location: Telluride, Colorado Airspeed: 180 kts Altitude: 12,000 ft MSL

Co-pilot: "Center, ABC has airport in sight."

Center: "ABC, Tower, radar services terminated, suggest you switch to advisory on 123.45."

Co-pilot: "123.45 for ABC." To me: "OK we’re on final, slow down to 140 kts and drop full flap."

I retard the throttle lever and wait for the airspeed to start decreasing. It doesn’t. "Alright," I say to myself, "raise the nose a bit, maybe it’s too low." The airplane begins to climb, airspeed changes slightly. Set throttle to idle. No change, we’re still climbing.

At this point I paused FSX and enter its controls configuration. I test out the control axes, everything is fine. Back in the cockpit I unpaused the simulation and hit the flaps, they deploy courageously against the airflow. I look at the throttle quadrant as I move my throttle lever back and forth, nothing. I then snap the view back to forward and incredulously look at the FD (Flight Director) light as it glows back at me as if to taunt me. I flick the switch off and I am again in control of my airplane. I slow down, land (luckily it was a long final leg) and taxi off to meet the limos waiting for my passengers.


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Making flight training more affordable

There is a lot involved in a flight lesson. While you may only log around 1.0 hours at a time, in actuality you will spend close to twice that at the airport. The pre-briefing, walk-around of the plane, startup/post startup/runup checklists and landing and stopping checklists all add up to quite a bit of time spent on the ground for which, while the engine is running, you’re paying.

I plan on finishing my private licence this summer and, being a student and having just bought a car, I need to make the most of each minute of each lesson.

I found the following tips on Jason Schappert’s M0A blog and I’ve paraphrased them for your perusal. Make sure to check his post for an explanation of each:

  1. Fly often.
  2. When you’re not in a plane, chair fly.
  3. Ask for a debrief after a flight.
  4. Take time to study.
  5. Set S.M.A.R.T. goals (Specific, Measurable, Attainable, Realistic, Timely).
  6. Memorize checklists which are not often used (i.e. emergency checklists)
  7. Write down questions (and then the answers).
  8. Rehearse radio calls.
  9. Organize your cockpit the same way each flight.
  10. Be confident.

These are all great tips and Jason expands on each of them in his post 10 ways to make your pilot’s license more affordable. Also check out his 5 tips for better flight manoeuvres post.

Great stuff!

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