Saturday, August 1, 2009


When should you abort take-off? How far down the runway until you know you aren't going to make it? These are important questions to ask and I'm here to answer them.

I enjoy throwing a story in to illustrate that even with my time, we still can get ourselves into difficult situations. I was flying into a forestry strip which is 2000ft long with obstacles at either end. The strip is located on top of a mountain so density altitude is an important factor to take into account. I was flying a Caravan and hauling five passengers and gear out. Fortunately, it was around 10am and we weren't in the heat of the day. The ground was wet and the west end was soft.
After loading the aircraft, I fired up and started on my first attempt. For some reason, I was unable to produce full power and therefore aborted. Upon inspection, everything seemed to be in order so I tried once more. Again, I was unsuccessful and aborted the take-off. I called via a satellite phone to the office to talk to the boss. He asked if I had the inertial by-pass separator out and to close it. It's a flap that moves into the air intake to help prevent dirt from entering the engine. This adjustment of the airflow reduces the available power. Upon closing the separator I was finally able to get the aircraft to produce full power. On my next take-off run, I had full power but the aircraft wasn't gaining enough speed. Now remember the strip is only 2000ft so your decisions need to be made quickly. At 70kts, which is the rotation speed, I had to abort the take-off as I knew I wouldn't make it. Hammering on the brakes and putting the aircraft into full reverse I was able to stop just in time. I knew I had to do something different if this was going to work. A trick of the trade used often, which isn't in the POH, pilot operating handbook; on the back track, as you turn the aircraft around, apply full power so that the aircraft's engine is at top speed as you finish the turn. Also you will be moving at that point and can sling shot yourself around the turn. Having momentum without using any runway up is a benefit for obvious reasons. On this final run, I hit the corner really moving and gaver the juice. As I built up speed I knew it was going to be close, and it was, as the "oh shit feeling" came on strong. On the caravan, you take-off with 20 degrees flap. On this last run, I left the flaps up until I had built up some speed then deployed them. Another trick I use on occasion is to throw down another 5 degrees before you run out of runway. It will give you a little boost to help you pop over the trees. Now this isn't a recommended procedure, and you should have someone experienced with this procedure to properly demonstrate it. This was an exciting trip and to top it off, on my return I had to file IFR, instrument flight rules, as the weather had moved in and I was unable to fly back visually.

Having so much stacked up against me, it's important to learn something from these situations. My aircraft wasn't overloaded but with the strip condition and the higher altitude, it made the take-off a challenge. With regards to knowing when to abort there are some indications to look for.

1) At the half way point your nose wheel should be off the runway. You want it just off the strip to reduce drag and not to high that the wings are slowing you down.

2) You can feel the aircraft start to lift slightly as it's almost ready to lift off. You want this by the time you are 1/2 to 3/4 of the way down. This should give you enough time to get the aircraft off into ground effect and climb out to avoid the obstacles.

3) Winds are extremely important, take-off into wind whenever able as this will greatly reduce the ground roll.

4) Strip condition - again if there is a soft end, take-off from the hard surface first as there is less resistance and you will be able to gain more speed in less time.

5) If you know it's going to be tight, back track the entire runway and at the end when you turn around, ensure you have full power as you finish the turn. This will sling shot you down the runway as you are carrying momentum around the turn. Take note, if you are flying a single engine Cessna, make a left turn at the end. You will be using the asymmetric thrust to your advantage.

These are just a few strategies that I have used in the past and still use today. Fly safe and keep it rubber side down.


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