We are all spacefarers, hurtling through space whether our
feet are on the ground or traversing through the air. Humans were meant to fly
but with artificial wings. Once you have broken the surely bonds and catapulted
through the air, there is no turning back from that delight. The desire forever
haunts you for more.
But when there is silence from the artificial means of
thrust, we want to get down and kiss the ground too. And therein lies a tale of
nonfiction.
Engine Out procedures are practiced daily by scores of
students and those undergoing recurrent training. But… but, and here is the
logical question, does that practice translate to the real thing? Mostly, I
hate to say…Depends!
The answer is quite simple, really. If you practice “feel
good” maneuvers, then the real live scenarios, when they come your way one day, the
mind will be rattled. Practicing good real world scenarios with a fund of knowledge in real world is
like executing a bicycle ride. Let me add in some comforting mathematics and
some simple calculations along the way to make it more palatable.
But one thing is for certain, to be able to come out of such
a real live scenario without a scratch, it is only the prepared mind that will succeed.
Look into your POHs and you will find some evidence in the
Performance section of your aircraft’s abilities. One such ability we need to
hone in on. It is Glide Speed. The first and only major thought in any engine
out scenario is to trim for best glide speed based on the weight of the
aircraft. (direct relationship - Heavy
weight = higher glide speed) most POHs will give you relative glide speeds for
different aircraft weights.
In most General Aviation aircraft, the glide distance per
1000 feet varies between 1.5 nautical mile to 2.1 nautical miles. It also
varies significantly with whether the gear is extended in complex aircraft, the
propeller is low RPM and if the flaps are retracted. Adding any drag significantly
affects the glide distance.
Altitude is always your friend. There is inherent Kinetic
Energy in an object in the air with or without thrust, the gravitational pull
gives it that energy. Dissipating the energy by virtue of the airfoil (wings)
gives us the distance gained per altitude lost. Knowing that one can quickly
calculate how far one can successfully land and fly another day.
Keeping brevity in mind, let us look at the common scenario.
Let us say a pilot loses the thrust at 5000 feet AGL. What are his chances? If
we multiply the 5 (000) x 1.7 = 8.5 miles is the answer. Simple and direct. This
encounter would favor the prepared pilot and not the panicked one. Of course
one has to go through the checklist at that altitude: Fuel (Change tanks &
Auxillary pump on for a short time), Spark (Check Magnetos on both) and
Air(Pull Alternate Air). If not successful, declare an emergency and plan for a
on or off-airport landing.
Now the easy math part I mentioned earlier. Look at the
altitude, your best glide speed and calculate the distance. Remembering that, that distance is in zero-wind condition. Add the prevailing wind speed and the decision
making becomes a little bit more complex. Heading into a header will obviously
diminish the glide distance, since one must add at least ½ the wind speed to
the glide speed to traverse the distance and that will reduce the overall
distance. However, if the airport or landing zone is on the leeward side, then
flying distance will increase by the factor of the wind. I have calculated a chart
attached to this article that might help most GA aircraft based on their
descent rate and the glide distance per 1000 feet.
Now for the practical test itself. I have done several simulated
engine-out scenarios both in flight simulators and in real time. The margins
are definitely lower in real world scenarios, because the pilot's mind plays tricks too. So those pilots thinking that 2.1
miles/1000 feet of altitude loss is their bird’s "Glide Distance" value, should consider a more
conservative measure at say 1.8 miles/1000 feet. Arriving over an airport at a
1000 feet is infinitely better that trying to do the most dangerous of all
things; “Stretching a glide” to the runway. “There it is! There it is! Oops!
@#$%$!
If you wish to have .pdf copy of this image, please request under comments.
Two methods of practicing are helpful. One is to spiral down
over the runway, if you have arrived there with altitude to lose, using the fighter pilot "flame out" technique of “High Key, Low Key and
Base Key” and the other is the straight-in approach. Both have different
calculations. In the former method, based on Altitude loss per 360 degrees turn
at 20-30 degrees bank angle must be known and that establishes the “Keys.” So
if your aircraft loses 1000 feet in a 360 degree turn, then the start with an
upwind “high key” at 1500 feet to arrive at the “low key” (Downwind) at 1000
feet and “base key” at 500 feet. In the latter method, it is based mostly on
the distance gained per 1000 feet of altitude loss. So at 9000 feet losing 1400+/-
feet/minute (heavy drag), one can traverse 11 miles of distance and that increases with a
tailwind and decreases with a headwind component.
Some basic CALCULATIONS on a very “Draggy aircraft” that
might help include the following:
((nm flown) * (feet
per nm)/ Altitude in feet AGL)) = GLIDE RATIO
eg: 11 * 6072 / 9000 = 7.42 : 1
(Distance in nm/speed in knots)*(minutes/hour) = TIME ALOFT
eg: (11 / 100) * 60 = 6.6 minutes
(Altitude in AGL)/(minutes aloft) = SINK RATE
eg: 9000 / 6.6 = 1363 feet per minute.
There you have it. Next section, I plan to discuss “Engine
Out” Scenario in an IFR state of mind. And that gets very interesting but no
less challenging and mathematically easy to accomplish safely if one keeps one's wits orbiting around one’s head. So let the knowledge and experience shoot up
in the air and the roots dig deeper into the ground for familiarity and
retrieval.
Safety is No Accident.
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