Each month in the back of this magazine, 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.
Our January 2007 issue 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.”
Jeb Burnside is this magazine’s editor-in-chief. He’s an airline transport pilot who owns a Beechcraft Debonair, plus the expensive half of an Aeronca 7CCM Champ.