Anonymous asked: 1st procedure for engine failure for a C172 is to maintain airspeed 65kts which means we have to pitch up to reduce the airspeed and descend when the airspeed descend to maintain at 65 (all while trying to restart the engine). why do we have to do that instead of continue gliding and descend only when the airspeed drops to 65?

Oooooo a technical question. I’ll preface this by saying I don’t have a ton of time in 172s, maybe 10 or so hours, but I’ve got about 1000 hours in Archers which I would consider analogous.

Okay, so, engine failure, first step is to maximize your range by maintaining best glide airspeed, the highest lift to drag ratio (or L/Dmax) which is in this case 65 knots. Your question, as I understand it, is why pitch up to attain 65 knots rather than stay level, bleed airspeed off down to 65 knots, and THEN begin the glide. Truth be told, I don’t know that I’d necessarily recommend that as a procedure but I could maybe see the logic behind it. Does Cessna recommend pitching up or did your instructor tell you to do it this way? I used to teach maintain altitude until best glide THEN descend however perhaps your instructor told you to do it this way because you were allowing the aircraft to descend before reaching 65 knots (it’s easy to do if you aren’t ready on the trim as airspeed decreases). Descending too fast with an engine out is one of the worst things you can do, but then so is descending too slow.

The thing you’ve gotta understand is that any speed EXCEPT 65 knots is going to cause you to lose altitude faster than 65 knots would. Faster and you’re adding parasitic drag by steepening your angle of descent. Slower and you’re adding induced drag plus you’re reducing distance covered with altitude lost.

So by pitching up to attain 65 knots you’re doing two things: 1) You’re lessening the drag on the airplane faster, minimizing altitude loss, and 2) Depending on your speed, you’re probably actually gaining at least a little bit of altitude (maybe a couple hundred feet or so). Altitude equals time in this situation and time is your friend. The higher you start from the more options you have to either get the engine restarted or stretch your glide to a suitable airport or landing area. Not necessarily the way I’d approach it but I can see the value.

The thing is though, and I’m just spit-balling here, what’s the average cruise speed of a 172? Maybe 90-100 knots? That’s not so substantial of a difference that I think you should initiate an aggressive pitch up to reduce airspeed. In most situations I’d say simply maintaining altitude, applying aft trim as airspeed bleeds off, and then beginning a glide at 65 knots is a perfectly acceptable procedure. However, the most important part is to make sure you don’t lose a single foot of altitude until that airspeed all falls off. You gotta pull!