What is the steepest glideslope your plane could fly?

That reminds me I’ve long been thinking to try the utmost sideslip I could go in zero wind. Not sure though how I could measure my glideslope, even if I could spare some attention for my spartan dashboard. Its readings wouldn’t be worth very much, anyway, under those conditions, the pitot being side-blown (or side-sucked?) and the static too slow on quick changes. Post-flight analysis of gps logs might me interesting, though. If the powers that be will consider such data sufficiently reliable.

This is steep:

Just a guess, for the steepest glide angle at optimal glide speed you´d have to look at the WW1 Fokker triplane. Or for other biplanes like Bücker Jungmann, Jungmeister, Stearman or similar. In an engine emergency these nevertheless will be landed at any suitable field with dead stick, no option for powered approach. So why would I want to do all approaches with power on and say 3 or 4 degrees glide angle if I don´t have to do that due to PAPI requirement or IFR landing ? This is a very bad strategy because in case the engine died you will find yourself on a brick wall or in the forest with no option at all , no chance to reach the airfield and no other space as you are too low for alternatives. Instead if you keep your traffic pattern altitude close enough to the airfield to glide there at idle revs , no problem if the engine stops. I guess most of you will fly cross country at a safe altitude of at least 1000ft agl to have a little longer for options so why throw that away in a flat approach ? Sure, a flat approach is an easy way for a good landing but you will not be in a good training state if you never do a steep/gliding approach – as we did in ALL landings at idle while doing the PPL at our school from the first flight. Mind you, it´s all about VFR, not IFR procedures. Our instructor, a former Soviet AirForce Major, was a bit uneasy about our usual idle approach but finally had to accept our logic. You will realize in that very second that you are done when you run out of time, altitude, and ideas, all at the same time ………….. Vic

P.S.: The Pilatus approach is not really at best glide speed ……..

The reason some jets can’t do the steeper approaches at places like London City is to do with paperwork not physical limitations. They usually need an AFM supplement for steep approaches and it’s often too expensive to do considering the limited places which are so steep.

That being said there are limits, and the circle to land at Annecy puts you on runway 22 with the PAPIs at 5.3 degrees (9,3%). It’s getting close to a glide approach in a Citation 525A with gear and landing flaps, although there are always the speed brakes if you need more drag.

A TB10, power off at 90kts and full flap, will drop out of the sky at 1200FPM – about a 13% gradient. Obviously you don’t want to fly an instrument approach like that because there is no way to correct if you get high. I reckon a 6% gradient would be easily controllable with full flap and a bit of power. My usual instrument approach – clean at 100kts would definitely not be flyable.

I have noticed that as power drops off for a steeper approach the aircraft becomes less pitch stable – I assume this is because there is less propeller wash over the horizontal tail surface.

Perhaps we should try flying this using GPS-ILS: It would be easy to set up a range of angles.

Presumably a limitation with jets is partly the need to keep some power on, so that they can spool up quickly for a go-around. Piston engines should respond more quickly; maybe some of the modern jets do too?

For RNAV approaches, TERPS criteria are based on aircraft approach category and have the following maximums:

Category GPA
…..E……….3.1
…..D……….3.1
…..C……….3.6
…..B……….4.2
…..A……….5.7 (6.4 for 80 KIAS Maximum)

While developing technique, and training in the C 182 amphibian, at 3350 GW, I determined that a 20 flap power off approach is best flown at a 12 degree approach angle, from which a very pleasing power off landing can be made. It would be steeper with 40 flap, and the transition to a decent flare would become critical. I had similar experiences while flight testing a modified Caravan, with a huge addition to drag. The “braking” effect of the prop at idle was a big effect too (see MT thread running). To acquaint ones self, with steep approach angles, view some helicopter autorotation videos – much steeper than 12 degrees!

This becomes a critically important aspect when considering an EFATO. To transition from a high power climb (possibly at too slow a speed (Yx)) to a good glide is going to use up a huge amount of altitude, which will artificially affect the total glide angle. Shock cooling and traffic considered, practice glide approaches from altitude. When you get really comfortable with them check your approach angle, it may startle you how steep it is!

Shock cooling is not an issue when you have worked down to traffic pattern altitude , the rest in a gliding mode to the landing strip will not do any harm – if ever a shock cooling exists. Para dropping aircraft or glider towing aircraft should definitely have an issue here – but do not obviously ?!? I don´t care about any angle, I watch the gliding speed at idle for the final, that´s all. Vic