It occurred to me the other day that while humans are not
meant to fly, we have through our intellect and perseverance learnt the physics
of how to fly like birds, that is, without wings attached to our bodies,
although with the Jetman-age, that might be disputed.
But what happens when the propulsion system gives up the
ghost and the only salvation is to find a place to settle down on the terra
firma. Unlike birds alighting on a treetop, planes do not necessarily like the
idea of treetops or trees in general (well insurers surely don’t). So that
brings up the discussion of how to “alight” on the green earth with all limbs
and wings intact.
The major issues we need to discuss are what would you do if
you lost an engine at the following altitudes…
500 feet
1000 feet
2000 feet
5000 feet
10,000 feet
What would you do?
Let’s start with an “engine out” on the runway and get that
out of the way… solution is to close the throttle (pull it back all the way and
the mixture) and brake to stop on the pavement if possible, shut down the
electronics, Magnetos and evacuate the aircraft quickly! Alertness is the key. There
is plenty of fuel in the wings since you just took off and any miscreant spark
can make a mess of things quickly.
At 500 feet, the options are limited except flying straight
ahead with minimal degrees of bank, no more than 20 degrees (you don’t want to
lose the vertical component of lift). If there are trees ahead, slow the
aircraft to minimal controllable airspeed as you mush onto the treetops with
the gear stowed. This is an eminently survivable technique. For that matter if
you have to set the plane down on any terrain where you cannot fly out from,
leave the gear in the wheel wells. Dissipation of energy in a slow skid over
the terrain will reduce the harm from an abrupt 100-G force on a sudden stop at
70+kts. A 100-G force can liquefy the human body into a horrible mess. Thinking
about Force = Mass x Acceleration, Reducing the acceleration reduces the (G)
force. As a preplanning reminder at this juncture, one should always observe
the departure and approach end of every runway for potential unplanned
landing-sites. Use the 45-degree entry to evaluate both ends of the runway; a
good habit to say the least. Bad things happen even on runways when fuel
starvation is the cause and pilots and passengers sit and discuss what might
have been in their seats as trouble brews into a catastrophe. So, remember to
evacuate the aircraft as quickly as possible after an unplanned landing.
At 1000 feet more optional vistas open up to you. A turn
back to the crosswind runway or the same runway you departed from is a real
possibility. Only if you are astute and aware enough to take advantage of the
possibility. But here, practice makes it easier to walk away without a scratch
on pilot and plane. The most important thing is to immediately maintain an
appropriate Glide Speed (GS) for the weight of the aircraft. Scan the Fuel
flow, change to other tank, check magnetos on both and Alternate Air handle
pull quickly without a thought- these are Critical Memorized Actions! Then, using
the common heuristic, reduce 2 knots from the glide speed for every 100 lbs
less weight, since best glide speed is calculated at max gross weight. Careful
preflight planning to figure out the GS at various weights and have them memorized
might save the day too, someday. In some aircraft, you might only require a 3-4
degrees pitch down in others a steeper 6-7 degrees nose down maybe required to
keep the constant appropriate glide speed. The importance in immediate
recognition and execution of planned action cannot be underscored. Usually the
human brain has a few seconds of disbelief that colors the next move. These
seconds if prolonged are detrimental to a good outcome. Unless one has
practiced such a maneuver previously – and many times, it is difficult to
ascertain the big picture rationally as the ground rushes at you and the
altimeter winds down at break-neck 600-1000 feet per minute speed. So,
practice, practice, Practice! Remember it is better to fly and mush it gently
onto a surface then stall and spin like a missile into the ground!
At 2000 feet the options increase even more. Here, one has a
chance to figure out the three components that make the engine hum; Fuel, Spark
and Air. Commit to Memory! So, check the (Fuel) gauge and switch tanks + Boost
pump (in case of vapor lock or contaminant), Check the Magneto switch (Spark) is
on both and open the Alternate Air for (Air) induction. Most General Aviation
Aircraft have a glide ratio of about 1.5-1.7 miles of distance gained for 1000
feet of altitude loss. One can increase the distance based on the winds (tailwinds
behind you help get you to the airport or suitable landing area by extending
that 1.7 nautical mile (nm) to perhaps 2.0 nm with the same glide speed). To
increase the distance, Glide Speed is to be followed with a perfect trim (to
reiterate) and an appropriate pitch attitude to reduce drag. In a complex
aircraft, pulling back the propeller also helps the gliding distance by
reducing the propeller drag. In retractable gear equipped aircraft. Experience
counts in knowing when to bring the gear down as extension of gear increases parasitic
drag and makes the pitch attitude much steeper (reduces the glide distance). In
other words, a 3-4 degree, pitch with gears retracted and a gained distance of
1.8 miles per 1000 feet of altitude loss, becomes a 6-7 degree, pitch and 1.2
miles per 1000 feet of altitude loss with the gear extended and similar Glide
Speed.
At 5000 feet and above altitude, other issues come into
play. Although options increase in finding a favorable landing area, more
critical thinking is required. The longer the engine remains quiet, battery
power is drained due to lack of alternator helping juice up the battery or
batteries powering the many avionics in use. It is therefore beneficial if you
are within glide distance of an airfield to lower the gear early on and circle
overhead the runway to land. Foreflight type Apps also can help create a circle
around the aircraft to help determine gliding distance (If you have set them up
according to the aircraft you fly) based on glide speed and prevailing winds.
These Apps can be of great help. However,
don’t forget to put the gear down if you are extending your glide reach with
the gear retracted when you arrive at the airport either. Remain cognizant
of all the dynamics involved in flight. Multiple attempts to restart the engine
can be accomplished and if the recalcitrant pistons don’t start pumping,
continue with the old adage “Aviate, Navigate and Communicate,” or put simply,
fly the plane, look for NRST (Press the NRST button on your favorite GPS box)
landing site and talk to ATC while squawking 7700.
Those pilots flying aircraft with the landing gear fixed and
welded securely to the airframe, need to remember that reducing drag is a
simple mechanism of a properly trimmed aircraft without a slip or a skid and no
flaps deployment until runway of landing is assured.
In the next section, we can discuss some mathematics and
aerodynamic limits that work for us in flight and methods of reaching our
intended landing area safely.
Until then, be SAFE! And remember NEVER stretch a powerless
Glide. Bad things happen when you try to “pull up” to reach a landing strip.
Those things are buried in issues of Stalls, Spins, Crashes and NTSB statistics.
Remember venerable Bob Hoover’s simple statement, “Fly the aircraft all the way
to the crash site.” Ah, there is a lot of truth in that!
No comments:
Post a Comment