Each month, we chronicle recent accidents we hope are of interest to readers. A glance at a random month’s entries likely would reveal that a substantial portion of them involve total or partial failure of a piston single’s engine. Yes, there’s selection bias involved—we typically try to highlight the most educational accidents and incidents, and many in-flight engine failures don’t result in an event reportable to the NTSB.
But the evidence also points out that pilots frequently mishandle the event, perhaps just as they mishandled their fuel management, since many engine failures can be traced to fuel starvation or exhaustion. To be sure, mechanical failures that are no fault of the pilot also can fail an engine. Regardless of the reasons, once the engine quits, it’s the pilot’s job to manage the airplane’s remaining energy and come to a safe stop. There are some considerations beyond just flying the airplane, but let’s talk about that first, if only to get it out of the way.
We’ve all been trained in the engine-out glide. Typically, the instructor will have a field or even a nearby runway in mind as a destination when power is reduced, while the pilot focuses on maintaining airspeed and forgets to look around, especially out the other side of the airplane or even behind it. We all get a good laugh out of the pilot’s failure to find the best landing area, but there’s a lesson there, too, which is to not get fixated.
Early in the exercise, after we’ve performed all the remedial actions designed to restart the engine, it’s time to configure the airplane. It’s a rare engine-out checklist that advises extending flaps until a landing is assured, so unless the failure comes right after a flap-extended takeoff and they are the only thing keeping you in the air, they should remain stowed.
Same for retractable landing gear, on both counts. If the gear is extended when the engine quits, and time and altitude allow, retracting it definitely will eliminate drag over the long run, but there may be a temporary increase in drag as the gear cycles. No bueno at low altitude. In the case of a failure just after liftoff, leaving the gear down to absorb energy likely is a better tradeoff than retracting it. Cowl flaps, if any, and other drag-producing equipment—an air conditioning condenser, maybe; spoilers/speed brakes certainly—also should be closed/retracted.
What Speed To Fly?
While all this is going on, you also need to obtain and maintain an optimal airspeed. There are two possibilities: best glide speed, VBG, and best lift over drag speed, sometimes called minimum sink speed, and typically abbreviated to VLD. The former provides the greatest glide distance; the latter is for when you don’t care about glide distance but want/need more time aloft, as when soaring the mountain ridges in your Cirrus.
For typical light airplanes, manufacturers publish a single airspeed to fly in an engine-out glide. Some come with more than one number: Cessna publishes three speeds for the 172S Skyhawk SP: 70 KIAS for engine failure immediately after takeoff, 68 KIAS (labeled “best glide speed”) at other times and 65 KIAS when 10 or more degrees of wing flaps are deployed, as when landing without engine power. If no best glide speed is published for your airplane, it can be approximated by flying at the midpoint between best rate of climb speed (VY) and best angle of climb (VX).
These values typically are for maximum gross weights. In other words, unless the failure occurs on takeoff, true best glide speed will be obtained at some lower number. How much lower should that number be? The accepted rule of thumb is to reduce the published best glide speed by five percent for every 10 percent below maximum gross weight. As an example, my tip-tank-equipped Debonair grosses out at 3550 lbs. If it’s just me, full tanks and some gear, the airplane weighs about 3120 lbs. at takeoff. That’s a difference of 430 lbs., or slightly less than 13 percent. Half of 13 is 6.5; I should reduce my published best glide speed of 105 KIAS by 6.5 percent, or 6.8 knots. My weight-adjusted best glide speed in that scenario is 98 KIAS.
You can find these speeds on your own, of course. As the General Aviation Joint Steering Committee (GAJSC) wrote in a safety enhancement on the topic, “Start at VY or the manufacturer’s recommended best glide speed with power off…and note speed vs. sink rate as you adjust pitch to reduce airspeed. For the most useful results, you should do this as close to typical mission weight as possible. To identify minimum sink speed, look for the highest speed forward that will give you the lowest rate of descent.” (Disclosure: I worked with the GAJSC to help develop this and other powerplant failure-related safety enhancements.)
Finally, we should note that VBG and VLD occur at specific angles of attack. If you have an angle of attack indicator, use it. If not, fly at the appropriate airspeed.
Shortly After Takeoff
The worst-case scenario for an engine failure is right after takeoff. The airplane is relatively slow—perhaps below its best glide speed—and the immediate challenge is to get the nose down far enough to maintain that target speed. That can require a hefty push on the pitch control to establish the correct attitude without nibbling at a stall. Meanwhile, and thanks in part to related articles and a video by AOPA, plus a couple of recent accidents, there’s been an uptick of interest among some pilots, especially those hanging out in online forums, in turning back to the departure runway when the engine fails shortly after takeoff. It’s a natural desire to want to be back on the closest runway, but turning back—sometimes known as the impossible turn—can be the worst bad choice you have.
The January 2007 issue of Aviation Safety featured a detailed article by spinmeister Rich Stowell, “Turnbacks Reconsidered,” in which he wrote about the results of simulator-based tests flown by several pilots, ranging from 40-hour students to those with more than 200 hours. The simulator emulated the characteristics of a light, single-engine airplane with fixed landing gear and a fixed-pitch propeller.
According to Stowell, “a ‘successful outcome’ was defined as follows: In all cases, the maximum rate of descent could not exceed 2500 fpm, rate of descent at touchdown could not exceed 500 fpm, and bank angle had to be within five degrees of wings-level below 100 feet AGL. For turnbacks, the airplane had to complete at least 175 degrees of heading change without exceeding a 55 degrees of bank.
“One hundred percent of the attempts to proceed straight ahead (35/35) resulted in successful outcomes—pilots maintained control of the airplane all the way down to the ground every time. The probability of survival in an actual emergency: high….”
“By contrast, only 62 percent of all of the attempted turnbacks were successful (69/112). Thus, nearly two out of every five attempts failed. And the majority of failed turnarounds culminated in stall/spin departures [from controlled flight]. The probability of survival from the failed turnbacks: low. The probability of significant crash damage to the airplane: high.”
A host of other factors are part of the equation. For one, the longer the runway, the more likely may be a successful outcome if the airplane doesn’t have to glide as far to reach pavement. Another is the wind, since a stiff one will reduce groundspeed on initial climb, keeping the about-to-be-powerless airplane closer to the runway. When pointed back to the airport, that same breeze may provide a tailwind. Climb rate, wing loading, total drag, how quickly the reversing turn is made and how far the airplane is from the runway when the engine fails all factor in to whether a turnback maneuver will be successful.
Practicing engine-out glides can be dull and boring, but we can spice it up. Typically, the exercise starts at a healthy altitude and, after running the checklists and configuring the airplane, you descend until it’s obvious whether the chosen landing area could have been reached if the engine actually had failed. While engine-out glides certainly may be practiced solo, it helps to have an instructor along, or a safely pilot, to provide a critique and ensure you don’t forget something.
That’s especially true if you want to go out and do some testing to find the best glide and minimum sink airspeeds for your airplane at different weights, which we recommend. And we strongly recommend having an instructor along if you’re out practicing turnbacks. Of course, you’ll pick a quiet field for turnback practice, not a busy one where you can be head-on with departing traffic.
If you go out to practice turnbacks and/or engine-out glides, be sure to keep it realistic and account for the “startle factor” by waiting five seconds before reacting to the engine “failure.”
Tools You Can Use
The recent and ongoing revolution in portable computers and their aviation-specific applications has produced some worthwhile tools for managing the engine-out glide and even to help us avoid being out of gliding range to an airport.
As one example, the popular EFB app ForeFlight includes Glide Advisor™, a feature the company says uses “terrain, GPS data, winds aloft, and your aircraft’s best glide speed and ratio [to shape] a glide range ring around your ownship icon on the moving map display.” An example is shown at top right. By referencing the glide range ring in real time, a pilot can maneuver to never be out of gliding distance to land, for example, or choose a less-risky altitude.
At bottom right is a promotional image from Xavion, a situation-awareness enhancement app its publisher says “constantly imagines engine-failed glides to every runway in gliding range, and then shows you the safest-possible route as a Highway-In-The-Sky to take to an airport in the event of engine failure.”
Right After Takeoff: Where To Go?
Landing straight ahead or turning back to the departure runway are not the only options when the engine fails shortly after takeoff. Instead, consider establishing altitude and/or distance zones within which your response to an engine failure is predetermined. Here’s what we mean, adapted and condensed from Tom Turner’s October 2019 Aviation Safety article, “All Or Nothing?”
Until the airplane reaches at least 400 feet AGL, your only real option in the event of engine failure is to land almost straight ahead. You probably have less than a minute to prepare to touch down, less if you turn and create a horizontal lift component. Why 400 feet? This is the lowest altitude at which IFR flights are expected to make a turn when departing and is one we should be briefing anyway.
Between 400 feet AGL and about 700 feet, you may be able to turn as much as 90 degrees left or right to align with the best landing option. To survive this, you need to know ahead of time what that option will be. Google Earth or another resource can help you make this decision before takeoff.
Between 700 feet AGL and about 1200 feet, you are in the range where you may be able to turn up to 180 degrees to align with the best landing option. This may not put you back on the runway, but it might get you to level airport property.
Above 1200 feet AGL, you should have enough altitude to actually get back to the runway behind you if you do everything right. But you likely won’t know this unless you practice and make careful notes about climb performance, distance from the airport and turning rates. Regardless of the range and the options you attempt, when you glide back through 400 feet AGL, you’re likely less than a minute from touching down. Level the wings and land on the best option that’s roughly straight ahead, to help prevent a cartwheeling arrival that’s sure to do more damage to the airplane and its occupants than the straight-ahead alternative.
About The Propeller
In the January 2014 issue of Aviation Safety, Catherine Cavagnaro wrote about her test flights to determine if stopping a fixed-pitch propeller increases glide performance by minimizing the drag of a windmilling prop. Her research revealed an average 8.3 percent improvement in glide performance, the time it took to glide from 8000 feet MSL to 7200 feet at the airplane’s published best-glide speed. Speaking to the pilot whose engine with a fixed-pitch prop has failed, she wrote, “Should he or she decelerate below published VBG to stop the propeller and extend the glide? Possibly, recognizing that the benefit can be approximately eight percent greater glide distance, and that may put more suitable terrain in reach.”
However, it’s important to note these tests were performed under ideal, consistent conditions and no attempt was made to determine if the time spent at airspeeds slow enough to stop the prop affected the overall glide distance. The value of stopping the prop depends on a host of variables, but it can be worthwhile. Testing with your airplane will tell the tale.
For those flying singles with a constant-speed propeller, there’s an easy way to approximate these results: pull the prop control all the way back to its low-rpm/high-pitch setting when the engine fails and can’t be revived. You should be able to sense the acceleration. Caveats include that the prop may not respond after a failure in which engine oil goes overboard, since that’s the working fluid in the propeller hub. Also, don’t forget to return the prop control to a more appropriate setting before adding power after a simulated engine-out exercise.
This article originally appeared in the August 2021 issue of Aviation Safety magazine.
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The table looks realistic. According to my own experiences, the C172 can do 180 degrees with less than 500 ft loss. When you add reaction time and a small reserve, 700 feet seems like the right minimum. Another thing is whether it will be possible to return to the field. However, the most important thing is to think about the solutions in advance – situations change and the solutions must also adapt to the changed circumstances.
Coming in for landing at an unfamiliar airport you should note what your engine-out options will be after gassing up and departing. Left or right? At a known airport you should be intimately familiar with best options according to altitude on climbout. Finally, remember that there’s always a point on the earth you can glide to, regardless of altitude; it’s under you. When practicing engine-outs, start your scan for landing locations as close to your side of the plane and range out.
Loong time ago one of my instructor’s showed me a trick in my 108-2 at that time: find your best glide speed and put a mark on the windscreen….any spot under that mark you can reach to land…works at any altitude.
I practice that today, yes, but am very grateful that I have not had to use it for real (yet).
Mark the windscreen – where? Thanks.
From context, I think the idea is to find best glide speed, look for the stationary point (that everything appears to expand around) and mark that point on the windscreen (sharpie taped to a stick?). Then, any spot under that mark is one you can get to; any spot above it, you can’t.
I credit my successful engine out off airport landing to my glider rating. Once I exhausted all attempts to get the engine going again, my brain went into glider mode. Things like selecting a multiple field candidates scanning for livestock all came into play. Another glider fundamental was speeding up to land and bleeding off airspeed just above the landing zone also came into play. I strongly recommend that all pilots get some glider training. Your energy management skills will go way up.
… presumably he meant, “… mark the horizon on the windscreen”. Not a bad idea if straight-ahead is your best option, and you can reach that far.
As a general rule, I don’t worry about this at tower-controlled airports; there is a lot of real estate, and usually a lot of traffic, so there’s not much I can do to mitigate a departure engine-out.
At the smaller rural GA fields that I spend most of my time, I listen to the pattern traffic and decide whether to fudge left or right after breaking ground. My elderly C172A will almost always circle-to-land on the departure runway above about 200 feet, as long as I’m offset and turned away from the breeze. And having 40-degree flaps doesn’t hurt.
Shocking to me that the pilots in the pictured Comanche were seriously injured. Let’s install and wear shoulder belts, folks… Good glide management won’t help if your head hits the panel.
Good article but I have to wonder how the pilot of the PA-24 pictured managed to wreck so violently into a wide open field?
William makes an excellent point that installing a good set of four-point (at a minimum) seat harnesses in the front seats is your best defense against injury in an off-airport landing. It is probably one of the best investments you can make if your plane only has basic lap belts. Even on a flat, obstruction-free field like the one pictured, if the soil is soft or muddy, the plane is likely to dig in and come to a sudden stop. This is especially true with fixed gear and a nose wheel. Judging from the downward slant of the cowling of the PA-24, I would guess that the nose wheel either collapsed or dug in causing a rapid stop. It doesn’t matter how good your landing is, but how suddenly you come to a stop that will dictate your injuries. Conversely, landing on sand (as on a beach), the wet sand will support the plane better and dry sand is more likely to cause the plane to dig in.
Five point harness even better
There are a number of errors here (minimum sink airspeed is never equal to best L/D speed), but let’s stay positive.
1) Knowing that 100 fpm is almost exactly 1 knot makes estimating your L/ D *through the air* trivial: divide your airspeed in knots by the sink rate in knots (or fpm/100).
2) To get your L/D *over the ground*, tune your GPS to the destination and do the same math with the ground speed, not air speed, reading.
3) Doing the same math while climbing at takeoff power gives you the flip side of L/D, a climb L/D if you will. If this is less than the glide L/D, and it almost always will be with the higher wing loading planes, like a Bonanza, then you ain’t gonna make it back to the runway, assuming calm winds.
4) The Foreflight glide ring has two (possibly fatal) flaws. 1) It doesn’t know the real winds aloft and 2) it only knows the L/D at one speed. With a tailwind, going slower will get you farther than the ring shows, as will going faster into a headwind.
5) Manufacturers of power planes seldom, if ever, give a glide polar – that is the L/D at different airspeeds. A semi-criminal omission IMO.
6) A 180 degree turn will never get you back to the runway, somewhere on the airport maybe, but not back aligned for landing. For over half the turn, you’re going the wrong way. So the optimum turn is done at a 45 deg bank and at a speed *less* than best L/D. Without wind, you do 270 one way and 90 the other for a total of 360 deg. Other combinations can be chosen, but the total is still 360 …
7) unless there’s a crosswind and you turn *into* the wind. It will help blow you back toward the runway center line.
8) Don’t insist on a perfect landing or landing surface. In congested or wooded areas, anywhere on an airport beats anywhere off. And 10:1 farm fields beat any kind of road. The insurance company bought itself an airplane when that engine quit, don’t you buy the farm trying to save it money.
Yep, I’m also a glider pilot. We train for and practice low altitude returns. It’s a tricky maneuver and the odds that you get it right the first time without proper instruction are quite low.
Jeffry, dead on. Minor quibbles:
1) There is no such thing as “L/D over the ground”, despite the fact that glider pilots often use the phrase. L/D is the ratio of lift to drag and is unaffected by wind. What you’re looking for is “glide ratio over the ground” – a ratio of distance traveled over the ground to altitude lost
2) On the “more than 180 degrees” turn-back, some EAA guys have played with this and found that for most light planes, by the time they’re high enough to get back to the airport, the angle they have to turn is only slightly more than 180 degrees – it’s nowhere close to a total of 360. That was also my experience with practice rope breaks – and I’m sure yours: the additional angle is quite small. Numerical example: turning back in a relatively slow plane, 45 degree bank, 50 kt airspeed, the diameter of turn is 444 ft. If you complete the turn at 100′ AGL, you will float for about 1,000′ (probably more – you have to slow down from your turnback speed), requiring a turn of 26 degrees to get to centerline, plus 26 degrees the other way to straighten out, for a total of 230 degrees, not 360. If you complete the turn at 200′ AGL, you need only 206 total turning degrees. If there’s wind and you turn into it, those angles get smaller.
“But the evidence also points out that pilots frequently mishandle the event”
“best glide speed, VBG, and best lift over drag speed, sometimes called minimum sink speed, and typically abbreviated to VLD. The former provides the greatest glide distance; the latter is for when you don’t care about glide distance but want/need more time aloft”
Well, I guess that provides some evidence, right there, that even the people writing articles about gliding airplanes get confused.
VLD is the speed that provides the greatest glide distance. The speed for maximizing time in the air will be lower, often quite close to the stall speed.
While adjusting your speed for actual weight can help, it won’t make much difference because, as any mathematician will tell you, when operating close to a speed giving either a maximum (distance) or minimum (sink rate), small variations in the speed won’t make much difference at all to the distance/sink rate.
A point that is hugely important, and almost never mentioned, is that the altitude required to make an “impossible turn” varies as the SQUARE of the airplane’s turnback airspeed. This is why people who fly Piper Cubs think the “impossible turn” is fairly easy (because for them, it is) while people who fly Bonanzas and Cirruses and P51s think it’s difficult-to-impossible (because for them, it is). Turnback speeds vary from ~48 kt for light machines to 73 kt or more for heavier ones, and the square of that ratio is 2.3. So, if a light machine can turn back in 500 ft, the heavy one will need 1,200 ft. And, by the time the heavy machine gets to 1,200 feet, it may be too far away to glide back. What’s more, the turning radius also depends on the square of the airspeed, so the heavy plane will be displaced much farther to the side during the turn-back, and may need even more altitude to reposition laterally back to the runway.
Of course, the altitude required also varies as the inverse of the L/D ratio. For most GA airplanes the L/D is between 8 and 12, but for a modern sailplane it’s at least 30. Sailplanes also have low turnback speeds. As a result of both factors, sailplanes can comfortably turn back from 200 ft: this turn is not called the “impossible turn” – it’s called a “practice rope break”. It would be a huge mistake to try the same turn in a Bonanza.