A pilot recently had an engine out situation in a Seneca V.  Because he found himself landing long, he initiated a go-around.  He crashed, killing his entire family.

     A pilot of a military transport took off from San Diego.  The crew chief informed him that the right engine was on fire.  The pilot elected to keep the engine available for power if needed while he went out some distance to maneuver for landing.  On short final the wing spar burned through and the plane crashed.

     What do these and many other twin related accidents have in common?  They show a fear on the part of the twin pilot that there might be a problem reaching the runway for a safe landing if only one engine is operating.  We have this fear because we know from our training experience how poorly twin engine aircraft, especially light twins, can perform under certain conditions with an engine out.  It takes a well trained very competent pilot to handle a worst case scenario immediately after a takeoff engine failure in a general aviation twin.

     However, if the failure occurs at more than 300 feet altitude, probably attained less than 30 seconds after liftoff, the power relationships during engine-out cruise and landing are extremely different from the worst case scenario all twin pilots are familiar with and afraid of.  Understanding these relationships and utilizing a simple, easily learned procedure which avoids undershoots and overshoots on approach and landing will make it easy for any twin rated pilot to safely fly and land on one engine.  The key operative word here is “easy”.

     Let’s consider a 4,000 pound twin with two 200 horsepower engines that, with best technique can climb 250 feet per minute on one engine at gross weight at sea level in standard air (cool 59°F.).  It physically takes 3 horsepower to raise 1,000 pounds at the rate of 100 feet per minute.  That means the example aircraft is receiving 30 horsepower (i.e., 3HP/1000lbs x 4000lbs x 250fpm/100fpm) over what it takes to fly level at that speed on one engine.  Because propeller efficiency is lower at low speed and high power, let’s say 80% rather than 85 or 90%, the engine is furnishing perhaps 38 HP in excess of what is needed to fly level.  Apparently this aircraft needs around 162 HP (i.e., 200-38) to fly level.  That means that if you simply hold altitude and don’t try to climb, you have available in reserve about 23% more horsepower (38/162) than you need to fly level.  Who couldn’t handle the aircraft under those conditions?

     After you find that you do not have the use of one of your engines and have done what you need to do to clean up and continue on one engine, you should fly the airplane in only one of two ways.  I will call these CRUISE mode and APPROACH mode.  

     CRUISE mode is flown with the bad engine feathered, prop approximately perpendicular to the wing, no flaps, rudder trim to reduce the pedal pressure needed to control adverse yaw, cowl flap closed on the bad engine, open on the good engine, and at or above best single engine rate of climb speed.  

     If the speed inadvertently drops below this, do not rely on power to recover.  Descend to quickly convert altitude to airspeed.  It only takes a descent of 76 feet to go from 80 knots to 90 knots and if you have excess power available, the descent will be less than that.  

     If the airplane can climb a little bit, that’s fine.  If it can only hold altitude, that’s fine.  Even if the aircraft is descending, that’s fine too.  If you’re only 2,000 feet above the ground and losing 100 feet per minute at full power on the good engine, you can go 30 nautical miles at 90 knots before reaching the ground.  Surely you can find somewhere to land in a 30 mile radius.  Besides, at lower altitudes, less power is required and more is available so your sink rate would decrease at lower altitude.  With an unsupercharged engine, a decrease in altitude of 1000 to 1500 feet might eliminate a 100 feet per minute sink rate.

     CRUISE mode is how you will fly the airplane until you are in position to commit to a long straightin (no final turn greater than 30 degrees) approach and landing.  Then you will fly in APPROACH mode.

     This brings up a most important rule of flying a light twin: never do a go-around.  The one(s) you did with your instructor should have told you that.  Think what that would have been like at gross weight on a hot day!  Tell the controller you will wait until he’s ready (if it’s safe to do so) but once you start down on final you will land on top of it, either side of it, under it, or through it, but you are not going around.  Don’t even think about it.

     A transport category aircraft such as an airliner or jet has plenty of excess power on one engine, along with quite high landing speeds, so in that case if there is any question, go around.  Not so in general aviation light twins—many pilots have tried, only some have succeeded.

     The secret of safe engine-out landings is avoiding undershooting or overshooting and the process is actually easy when done as described here.  An aircraft holding a given airspeed can descend at a minimum angle (of zero if there is enough power) or a maximum angle, or anywhere in between.  If you try to descend at a steeper angle than the maximum, you gain airspeed.  Now estimating these angles is very difficult but you get the same information by using your rate of climb/descent instrument.  We must determine a sink rate between the maximum and minimum that gives us as much leeway as possible to correct either an overshoot or an undershoot in our approach.  This leeway is what gives us our safety and makes the approach and landing easy.

     To do this, you need to do some simple, safe testing of your aircraft’s performance.  Simulate approach configuration by putting the gear down, flaps as recommended, and reduce power on the critical engine to idle (not zero thrust).  With the aircraft preferably near gross weight and while maintaining approach speed and full power, high rpm on the good engine, determine the sink rate.  This is the minimum sink rate of the APPROACH mode.  If the aircraft holds altitude or climbs, use 50 feet per minute as the minimum sink rate.  Then determine the sink rate with the ‘good’ engine at idle power and the ‘bad’ engine at zero thrust.  This is the maximum sink rate of the APPROACH mode.  Assuming 150 physically available HP in our example aircraft, there should be a minimum difference of 1200 vertical feet per minute between full power and idle at 90 knots.

     If the flap setting isn’t specified, use no flaps.  What you want is the greatest difference between minimum and maximum descent angles so you will have more leeway to correct your first guess on the approach if it brings you in longer or shorter than you anticipated, which it probably will.

     How can you determine zero thrust?  You may be able to get a good idea by synchronizing the props at full RPM and around 14 inches of manifold pressure.  Maintain approach speed and slowly reduce power on the critical engine.  When the props begin to go out of synch because that engine is not able to maintain rpm, you are at or very near zero thrust power on that engine.  Use that manifold pressure to simulate the zero thrust roughly equivalent to a feathered engine.  

     Now that you have determined the minimum and maximum sink rates in APPROACH mode, you must select the APPROACH sink rate.  Try multiplying the minimum sink rate by the maximum sink rate, multiply this by 2, and divide this by the sum of the minimum and maximum sink rates.  This gives a sink rate at approach speed that puts you on the ground about half way between the farthest distance you could go at minimum sink rate and the shortest distance in which you could get on the ground at maximum sink rate.  

     For example, if the minimum and maximum sink rates are 150 and 1200 feet per minute respectively (unlikely numbers chosen to make a point),

     (150 x 1200 x 2) / (150 + 1200) = 267 feet per minute  

for the APPROACH sink rate.

     If this number is much less than 400 feet per minute, you will have a lot of leeway but your flat approach may be almost through the tops of the trees for the last two miles.  If that is the case, try dividing the maximum sink rate by 3 for use as your APPROACH sink rate.  If this is still less than 400 feet per minute, use 400 feet per minute for APPROACH sink rate.  APPROACH power is that power (one engine) which produces APPROACH sink rate in APPROACH mode.

     To go from CRUISE mode to APPROACH mode, lower the landing gear, move the rudder trim toward neutral if feasible, set the prop control at high RPM if it isn’t already, and switch to the normal approach speed, using elevator to control airspeed exactly.  Go to APPROACH sink rate by using APPROACH power.

     Use the normal approach speed for the configuration and conditions.  No more, no less.  Do not use an increased approach speed. This is what tempts go arounds.  An increase of only 10 knots, when including ground effect, will be roughly the equivalent of coming over the fence 100 feet higher than normal.

     You will change from CRUISE mode to APPROACH mode and APPROACH sink rate (and power) when you reach the point where you think that doing so will bring you exactly to your selected touchdown spot.  You need to have an idea what this sight picture will look like.  

     At a constant sink rate and speed, the point where you will reach the ground is that point in front of you that does not change its vertical angle relative to the horizon, i.e., it does not move up or down in your view.  Points beyond the touchdown point will gradually appear to move ‘up’ toward the horizon, points closer than the touchdown point will move ‘down’ (and eventually under) in your view.  

     On a low wind day, make several descents from different altitudes until you can determine roughly where your touchdown point will be when you fly at APPROACH sink rate and airspeed.  This can be simulated with two engines.  In a real engine out situation, if you guessed right, you will proceed exactly to your touchdown spot with nothing else to do except possibly reduce rudder trim, flare and land.  Keep it simple.  

     You probably cannot hold altitude, even at full power, in this APPROACH mode, but who cares?  You don’t need to hold altitude because you are going to land and you are not going to go around.

     Of course, most likely you will find you are somewhat overshooting or undershooting your intended touchdown point by noting that it is moving slowly down or up, respectively, in your field of view.  Remember your initial sight picture (angle).  For example, if you are undershooting (touchdown point moving up), add substantial power to quickly get back to your original sight picture, which obviously was a little inaccurate, and continue this power for a few seconds more until you have a slightly steeper sight picture of the touchdown point.  Then return to APPROACH power (and sink rate) and see how you do.  If, for example, your touchdown point is now moving down a little in your view, you are now overshooting somewhat.  Reduce power substantially to quickly get a sight picture between the last one and the original one, then return to APPROACH power (and sink rate) and again evaluate the sight picture.  

     For example, if you change just from 400 feet per minute sink rate to 100 feet per minute sink rate for only 5 seconds and then back to 400 feet per minute sink rate, at 90 knots you will extend your touchdown point by about 750 feet!  If you go only from 400 feet per minute to 800 feet per minute sink rate for 5 seconds and then back, you will shorten your touchdown point by about 760 feet.  Do you suppose you could do this?

     When correcting, do not just add or subtract a little from APPROACH power.  That would be equivalent to being low flying the ILS glideslope and just adding a little power hoping you will be back on the glide slope by the time you reach the ground.  You must return to the glide path such that flying at APPROACH sink rate (power) will bring you almost exactly to your chosen touchdown point. The point of coming in at the APPROACH power and sink rate is that at all times you can easily correct an overshoot or undershoot tendency, usually with only moderate changes in power to quickly change your sight picture to that which allows APPROACH power and sink rate to take you to your chosen touchdown point.  Although this should never be needed, you could even go to full power or idle power on the good engine.

     If you practice this once or twice (you can use two engines if you stay within the maximum and minimum single engine sink rates you determined), you will probably only need a couple of adjustments.  Thereafter you will fly the last couple of miles or more with no changes until over the fence and flaring for landing.  You use the long straight-in approach because this gives plenty of time to recognize and evaluate the sight picture and plenty of time for the power changes to take effect.

     If there is a substantial difference between approach and touchdown speed, sight for the end of the runway.  If there is not much difference between approach and touchdown speed, sight for a point a couple hundred feet down the runway.

     The above is about VMC operations.  If in IMC or following a VASI in an aircraft with mediocre single engine performance, you might wish to stay in CRUISE mode (but appropriate approach speed) until you break out, then hold altitude until the sight picture says that APPROACH mode is now appropriate.

     Since you normally touch down with little power and immediately power off, you will find that this landing is just like your others.  In fact, if you do it this way, it will probably be better than most of your others.  

Stop Twin Accidents

Dr. Sherwood Kaip

El Paso, TX

<skaip799@gmail.com>;   cell: 1 (915) 309-6340

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