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Best Glide Speed

When the engine stops, some numbers are more important than others -- but so are some actions. As pilots, we don’t talk through this problem nearly enough...

When the engine stops, some numbers are more important than others -- but so are some actions. As pilots, we don't talk through this problem nearly enough, which is too bad, because if you don't know what you are going to do when the engine quits, you may lose precious time -- and altitude -- as a result.

To get an idea of how not knowing what you need to do can result in a bad outcome, lets compare two case studies. In both cases, our pilots will be flying a FarFlungWorks Kestrel, which is a single engine retractable plane. The plane is fast and a bit on the heavy side, but has a good reputation.

CASE 1 (right actions, wrong thinking)
Our pilot is flying at 5000 feet AGL, when he detects signs of engine trouble. Before he can identify the problem, the engine dies in flight.

OUR PILOT DOES THE RIGHT THINGS -- He gets out his POH and flips to the emergency procedures. Well, that is HE TRIES to, but in his haste, he goes past the procedures a few times, and finally finds them. His altitude is now 3000 feet and falling. A minute has gone by in time, as he reads the checklist items. As he reaches the bottom of the checklist, he re-trims the plane for the best glide speed of 102 knots. The airspeed slows, and -- at that instant -- he regains a little altitude.

THE PLANE IS NOW AT 2000 FEET AND FALLING SLOWER, but it is still gliding toward the ground. According to the manual, the Kestrel will fly for 1.4 miles for every 1000 feet of altitude it will lose at the published Best Glide Speed. Since all the attempts to restart the engine have failed, our pilot turns to his trusty GPS receiver, and selects the NEAREST function. Unfortunately, the nearest airport is 4 miles away; just outside of the aircraft's best glide range. As a result, the plane makes an off-airport landing and is substantially damaged.

CASE STUDY 2 (right actions, right thinking)
Our pilot is flying at 5000 feet AGL, when she detects signs of engine trouble. Before she can identify the problem, the engine suddenly dies in flight, leaving her with a spinning prop and losing altitude.

OUR PILOT DOES THE RIGHT THINGS -- She immediately trims to the best glide speed for the plane, increasing the altitude to 5,800 feet by trading speed for altitude. She looks for a landing spot and searches for the nearest airport with her GPS, then she gets out the POH and turns to the emergency procedure. Because she has altitude and a little more time, she finds the checklist items and runs through them. As she reaches the bottom of the checklist, she verifies that she selected the correct best glide speed of 102 knots.

THE PLANE IS NOW AT 5000 FEET AND FALLING SLOWER. It's also already turned toward the nearest airport. Since all the attempts to restart the engine have failed, her focus is now on preparing for a power off approach and landing. Again, according to the POH, the Kestrel will fly for 1.4 miles for every 1,000 feet of altitude it will lose at the published Best Glide Speed. Again the GPS indicates the nearest airport is 4 miles away, which is well within the aircraft's best glide range from 5,000 feet. As a result, the plane makes an uneventful landing at the airport, leaving the plane undamaged.

SAME EVENT, DIFFERENT OUTCOME
Best glide speed optimize the aircraft's glide-range, but it alone will not optimize your critical performance as a pilot. There are a few other things you should think about if your engine stops producing power in the air:

  • FIRST, KNOW YOUR BEST GLIDE SPEED BY HEART. If you don't know it, you can get to it, but you probably will need the altitude you will lose while you are trying to find it!
  • SECOND, KNOW YOUR EMERGENCY PROCEDURES. You should be able to run through the emergency procedures without having to crack the manual. REMEMBER -- There are usually 3 or 4 emergency procedures per POH -- trying to find the right one in an actual emergency can be pretty hard!
  • THIRD, KNOW WHERE YOU ARE. Always have an out -- that's not just about weather. You need to know where you are all the time, so you can start heading towards an airport at the first signs of trouble.

BOTTOM LINE: By knowing your procedures you can avoid problems and, in many cases, make a safe landing at an airport. To be best prepared, practice frequently -- in your head -- running through the items of the checklist from memory while imagining various in flight emergencies. If you've seen it before -- even as make believe -- it will be less stressful when you see it in real life. Sure, there are cases where glide range is relatively unimportant (over water), but in those cases, the extra altitude will allow you extra time to call for help, declare an emergency, and pick out and align with the BEST off-field landing location. Off-airport, your chance of survival depends on how well you know what you're doing, the terrain ... and how quickly they find you.

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