December 8, 2016

Pounding it on, and other hard landings


Pounding it on, and other hard landings


It’s late May as I write this month’s article, and I find myself depressurizing after yet another successful semester of flying.

Why must I depressurize you ask? Well, the last month of flying for me consisted of giving flight checks to various levels of pilot certificate applicants (Private, Instrument, Commercial, Flight instructor, etc.). If you’ve ever taken a flight check, you have some idea of what a check pilot does, but trust me; it’s not necessarily a low stress job!

While I assume the applicant is properly trained for the certificate they are seeking, I am ultimately responsible for the safe conduct of the flight. Sometimes that means verbally intervening, but other times it means physically taking the airplane from the applicant.

Normally, taking control is not a big deal, but during landings, things can go wrong in a split second, so the check pilot needs to be ready to takeover at any instant.

Once in a while, the check pilot may let a student land hard, but they should never allow the landing to be unsafe. However, even we are not infallible and occasionally we misjudge when to take control, and the applicant “pounds one on.”

So what exactly is the difference between pounding it on and simply making a hard landing? Semantics perhaps, but we’re talking about relative levels of hard landings here.

Pretending you are the pilot applicant, let’s discuss this situation. If you feel your spine compress or you slip a disk that was a really hard landing!

Actually, if that happens, and you’re still not sure if it was “really hard,” check the wings. If you’re in a low-wing airplane, the gear struts will be protruding through the top of the wing. High wing pilots generally enjoy a little more give from their gear (not a good reason to switch to a high-wing however).

Bent gear struts or blown tires are also good indicators of a “really hard” landing. If any of these signs are evident, you will not pass your flight check. (I hope I didn’t need to spell that out!).

However, this doesn’t mean that you’ll pass if there is no evident physical damage to the airplane. Hard landings that make the check pilot say “Ouch, Oooh, Holy cow, Whoa, and/or Oookaaay,” may also end in a failed check flight.

In the absence of a verbal response from the check pilot, if you suddenly feel hypoxic right after touchdown it may be because the check pilot frantically inhaled all the breathable air just prior to your touchdown attempt. Don’t worry however, as he or she must now exhale to make the verbal response as previously indicated.

Despite the pilot’s natural inclination to give up after a hard landing, or be momentarily stunned by the impact, the critical response is to continue to fly the aircraft. Further loss of control will not help the situation.

Follow-through is the name of the game for successful completion of any landing, good or bad. Proper correction for crosswind conditions and steadily increasing backpressure on the control column during the landing roll will help maintain centerline and decelerate more expeditiously.

Preventing the pounding in the first place is the goal every pilot shoots for, but almost all fail to achieve at least once during their careers. Luckily, most pilots never damage the aircraft in the process, but I have seen a dozen or so hard landings that ended in the necessity for aircraft repairs (Luckily I wasn’t onboard!).

When it does happen, most pilots are at a loss to figure out exactly what went wrong and frequently blame the wind, or other environmental conditions. Sometimes, they’re right, but I’ve seen many a hard landing result from a sudden pull-up (too late, by the way) just prior to touchdown.

The usual scenario develops like this: the pilot approaches the touchdown with too high of sink rate and airspeed just above the absolute minimum. Just before touchdown he or she realizes the closure rate to the pavement is too fast and a final jerk on the control column is made to soften the touchdown. While this action usually succeeds in raising the nose so the nose gear doesn’t hit first, the landing is still hard. In battling a high sink rate close to the ground, even when the sink rate is adequately arrested prior to touchdown, if power is not applied and/or airspeed is already too slow, the touchdown is unlikely to be smooth. Even if the pilot realizes the need for power he generally underestimates how much to add.

The problem with late power application is that the change in angle of attack due to pulling the nose up dramatically changes the induced drag just prior to touchdown. The additional power required to maintain a safe airspeed to cushion the landing is thereby higher than would be required if the sink rate approaching touchdown was normal.

As a further example, consider the landing porpoise. There’s a reason that most aircraft are difficult to recover after the second bounce of a porpoise. The airspeed is at stall or lower due to the high angle of attack in the upswing of the second bounce; the aircraft is airborne basically because of the bounce, not because it is flying.

Addition of full power at this late stage may not allow for a recovery because the power available may not be sufficient to accelerate the aircraft fast enough to overcome the drag being produced; which is trying to bring it back down to the ground.

Deep stalls at altitude will similarly cause a loss of altitude prior to a full recovery even with prompt application of power. For these reasons, power application must be made early enough to preserve the energy required to flare for a smooth touchdown. If the touchdown phase is approached with insufficient airspeed and/or too high a sink rate, a go-around is in order.

Bottom-line, regardless of aircraft type, the ability to fly away from a low-airspeed, high angle of attack situation without touching down in the process is in part dependent on the amount of excess thrust available.

While all pilots will make a hard landing once or twice (or more) in their careers, lack of visual evidence of the incident does not mean that there is none. Internal structures can be overstressed such that there is no obvious external damage.

At other times, the external damage due to a hard landing is so subtle so as to be unrecognizable by the untrained eye. Very slight diagonal ripples in the upper wing skin may appear similar to other skin panels that have always exhibited unevenness. However, these ripples may be tell-tale signs of internal overstress.

I was once asked how to make a safe flight determination when there are no mechanics around, and to that I suggest a careful visual examination followed by a check of the ELT to see if it was activated. If the landing was hard enough to activate the ELT, I would think twice about flying it without an official “hard-landing” inspection first.

Bear in mind that it does not take a damaging landing to activate the ELT. So even if it was a slightly hard landing, you might want to check the ELT to make sure it has not been activated. Certain ELT installations are more susceptible to inadvertent activation than others and I have no good advice to give you on just how hard you have to hit to set one off.

Flight checks aside, landing hard isn’t the end of the world, nor does it necessarily mean you are less skilled than the next pilot. Sometimes the circumstances simply catch the pilot unaware and the hard landing is inevitable. However, there is no good reason why a landing should be pounded on.

If you hit so hard that you feel out of control in the process, something was not right about the approach to landing in the first place. Sometimes this is due to the conditions being beyond the pilot’s capabilities, but at other times it’s simply a skill consistency problem.

Consistency problems can be easily spotted as a marked difference in performance from landing to landing, even though the conditions are the same. If you fall into this category, get some assistance from a flight instructor to help you figure out what to change.

In the end, the key to consistently good landings is good initial training and much subsequent practice. Strive to make at least three landings every month to keep your skills sharp. Your aircraft will thank you for it in the long run!

This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 180 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.