Gliding Instrument Approach

~ Thomas Turner

Recently we looked at engine-failure case studies of aircraft that are close to identical in design and performance — except for the number of engines.  We discovered that significant, regular pilot training is needed to enjoy the safety advantage of a second engine.  Translation: For many pilots (those with ‘twin’ ratings, included) the single-engine airplane may actually be the safer machine.  And yet, regardless the number of engines, there’s still that pesky engine failure scenario, especially hazardous in the clouds.  If you fly a single-engine airplane, you need to prepare for the catastrophic power loss in instrument conditions.

Know the Drill

You can ‘drill down‘ your power-related emergency checklists to what the engine needs to run (fuel, air and ignition), and what you can do to manipulate those systems from the pilot’s seat (see previous article).  Memorization and practice.  Sit in the cockpit and feel your way through the steps. You need to know this cold should your engine die in flight.  This allows you to ‘fly the plane’ while you troubleshoot and transition to glide (see another previous article).

Engine-Out Approach

Worst-case scenario puts you in or above the clouds when the engine quits.  The cloud bases may or may not be high enough to allow much visual gliding before touchdown.  You need to fly an engine-out approach.

I had the amazing experience recently to attend Richard Kaplan’s Flight Level Aviation, at Waynesburg airport southwest of Pittsburgh, Pennsylvania.  Kaplan is well known in the Cessna 210 world, and operates one of the few full-motion single-engine simulators.  Although Flight Level’s 210 ‘sim‘ (actually, an FAA Level Three Flight Training Device) is configured generally for that type, the device mimics performance similar to most large single-engine piston airplanes.

The engine-out instrument approach is the ‘signature technique‘ of Flight Level Aviation.  Kaplan shows how to estimate glide performance and manipulate airplane drag to result in a ‘breakout‘ on short final to the runway.  His technique shows some surprising differences from what we’ve all learned about glides.  Kaplan’s points:

  • Most light airplanes’ published maximum glide is between 1.5 and 2.0 nautical miles for each 1000 feet of altitude loss.
  • Accounting for less-than-perfect, ‘under pressure‘ pilot technique, 1.0 nm/1000 feet is a conservative figure, easily used in the heat of the moment.
  • At five miles from the airport, then, you need to be about 5000 feet above field elevation.  Three miles out, you should be 3000 above ground level (AGL).  A one-mile final should coincide with 1000 feet AGL (INSIDER’S TIP: Here’s an argument for high cruising altitudes).
  • If flying an ILS glideslope, you need to stay above glidepath because your descent rate is greater than the 500-600 foot per minute required for a typical three-degree approach.
Kaplan reports that most pilots tend to glide TOO FAR and overshoot their target runway.  One of the most commonly necessary yet difficult things to do, he says, is to turn and fly away from the airport to make glide’s end coincide with the arrival end of the runway.  Although Kaplan teaches a standard-rate, 360-degree spacing turn (losing about 2000 feet in the process) — I think broad S-turns, still generally pointed at the airport and ‘stoppable‘ at any point if you’ve misjudged the approach, might be a better technique.

GPS

Many GPSs compute and display the ‘Vertical Speed Required (VSR)’ to reach a given waypoint (check your manuals!).  Hit NEAREST AIRPORT, adjust descent to match the VSR, and you’ll make the runway — just remember to hit your speeds.  If you know your panel-mount GPS well enough you can find the runway heading, put the GPS into OBS mode, and spin your course needle to the runway heading … and a moving map will display the extended runway centerline.

EMERGENCY IFR APPROACH: Many handheld units display extended centerlines too.  Now, if you have course guidance (the extended centerline) and glideslope (vertical speed required) information for a zero-zero emergency landing at any airport.  NOTE: If you turn away from the airport the VSR will be inaccurate and finally disappear (you’ll never make it pointed THAT direction!), but it’ll return when you turn inbound.

Speed vs. Angle

Fly the indicated VSR rate and aim for centerline … or if not GPS equipped, aim for the airport and compute 1000 feet AGL for every mile to go, using localizer and glideslope if available.  In many cases you’ll need to increase your descent rate to avoid blowing past the runway.  You’ll be sorely tempted to lower the nose.  Sure, that increases vertical speed, but it also boosts your ground speed, in turn requiring a greater VSR.  Instead, you may find you need to add DRAG (extend flaps, landing gear, etc. — in VFR conditions, the safest, easiest to correct method may be to enter a slip) and SLOW the airplane to get an angle of descent that puts you in position to land.  Many Pilots Operating Handbooks publish not only a Best Glide speed, but also a slower Minimum Sink Rate velocity.  Unless you’re aiming at an airport at the ragged edge of your glide capability, chances are you’ll need to be closer to the Minimum Sink to arrive safely.

BOTTOM LINE:  If you fly IFR in a single-engine airplane you need to practice the engine-out instrument approach.  The emerging world of computer-based flight training devices make this a far more affordable and available addition to your continuing aerial education.

Published by Thomas Turner