10/11/2016 – A couple of days after my day of exams I was back in the air. This time the lesson was on unplanned diversions.
Let’s say that you’re flying to an airfield, but when you get close and call for joining instructions, they say the runway is closed. In this case you will already have a diversion airfield planned (you will won’t you?) and you can pick that up off your plog and make your way there. That’s NOT an unplanned diversion, it’s planned for and hopefully executed well, when you need it. An alternate airfield should always be part of your preparation.
An unplanned diversion is when you’re not expecting to have to change plans but something happens in mid-air to make you have to alter your route. A typical reason would be weather. You’re flying along and realise that the cloud is lower than you expected, or a storm looks to be brewing ahead. You don’t want to just continue to fly into the bad weather so you decide to go somewhere else. But if you just casually head in another direction there’s a good chance you’ll get lost.
So to perform an unplanned diversion you need to examine your chart, pick a new spot, circle that spot on the chart, draw a line from your current position to the new destination, measure the distance, and work out the track there, and determine the actual heading required factoring in wind strength and direction.
All this while you are still flying the aircraft. Remember Aviate, Navigate, Communicate. It’s quite overwhelming the first time you do it (and not just the first time). The most important first step is to make sure you know where you are, and pick where you want to go to. You can orbit your current position while planning the diversion so you don’t end up starting miles from where you expected. If you’re struggling to control the plane and hold a pen and a chart and a ruler, you can probably use the rudder to steer, thereby freeing up your hands.
Once you’ve picked a new spot then circle it on your chart with your marker. You’ll be looking away frequently while planning so it’s good to be able to easily find it again when you’re ready to measure. Then using a short ruler draw a line from your current position to the new destination. Then measure the distance, a good rule of thumb is to use the end of your thumb, it’s probably around 9 or 10 miles on a 1:500,000 chart. (Measure this while you’re not in the aircraft and remember it!)
Then using the protractor work out the new track, and the wind to get your new heading and speed, and estimate the time to get there.
No, definitely not. But it can be made easier by using something like a DP-1 from Digital Innovations (others are available I’m sure)
This is a short ruler, protractor, has a Windstar and a table of common speeds showing times at each distance. I use the Windstar app every time before I fly and fill in my DP-1, it gives you for every 45 degrees what your amended heading should be, and the estimated speed at that heading. It’s usable in the air, unlike a CRP-1 flight computer!
Filled in mine looks something like this.
I mark an arrow to show where the wind is coming from. Then each box shows new speed on the top, and degrees to add or subtract from your heading. For example in the picture, you can see the wind is from WNW, so if my diversion was on a 90 degree track I’d be going 119 knots and have to head 86 degrees. If it was 225 degrees then I’d be travelling at 90 knots and have to head 235. After a bit of practice it’s pretty easy to use even while flying (and despite my terrible handwriting)
Of course once you’ve qualified you’ll probably end up using a GPS, but it’s still something worth keeping with you, and filling in before flight.
Performing an unplanned diversion in the air is stressful. It’s very easy to get overworked so it’s very, very important to keep FLYING THE AIRCRAFT. If you have to circle for five minutes while you get yourself settled it’s better than heading in the wrong direction.
I did a few unplanned diversions and managed to get reasonably comfortable doing them. We headed back to Gamston and the weather was looking fairly bad at this point over to our left. I casually mentioned to Luke that I’d just seen a bolt of lightning a few miles left of our heading at which point he took control and steered directly away from it. Storms are not something you ever want to get caught in!
If you want to know more, the podcast, as always, contains an expanded version of the above.