2017.0817 flying lessons · 17-08-2017 · to air safety investigators (asis), there are six basic...

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FLYING LESSONS for August 17, 2017

FLYING LESSONS uses recent mishap reports to consider what might have contributed to accidents, so you can make better decisions if you face similar circumstances. In almost all cases design characteristics of a specific airplane have little direct bearing on the possible causes of aircraft accidents—but knowing how your airplane’s systems respond can make the difference as a scenario unfolds. So apply these FLYING LESSONS to the specific airplane you fly. Verify all technical information before applying it to your aircraft or operation, with manufacturers’ data and recommendations taking precedence. You are pilot in command, and are ultimately responsible for the decisions you make.

FLYING LESSONS is an independent product of MASTERY FLIGHT TRAINING, INC. www.mastery-flight-training.com

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This week’s LESSONS: This sort of personal tragedy often gets overlooked among the 20 or more initial accident reports that appear every Monday morning on the FAA preliminary accident reporting system website. Yet it may have been one of the most common accident scenarios…and one for which

we rarely train.

The instructional flight had been operating for about an hour when the crash occurred. A local news source confirms that the airplane had just taken off from a grass airstrip away from the airplane’s home base when it crashed. The Pilot Receiving Instruction (PRI) and a passenger in the C172’s rear seats were seriously injured; the Certificated Flight Instructor (CFI) was killed.

See: https://www.faa.gov/data_research/accident_incident/preliminary_data/ http://www.newstimes.com/local/article/Reported-plane-crash-in-New-Milford-11750399.php#photo-13685275

I don’t publish photos of crashed airplane unless I believe the images are particularly instructive. This is a case in which we may learn a lot from looking at one of the photos, taken from the news source noted above. Six things stand out to me when I look at this image. Take a look yourself before you read what those six things are…

What did you notice in the photo?

My thoughts as a result of this image are:

1. The airplane impacted nose-low.

2. There is no indication of forward movement on impact—


no skid marks, no tire tracks in the turf. The airplane appears to have struck the ground nearly vertically.

3. The left wing is failed up and forward, while the right wing wrinkled but largely intact.

4. The tail is severely twisted, in the direction opposite that in which the left wing is bent. Yet the elevators and horizontal stabilizers remain intact—they did not hit the ground.

5. The flaps are partially and equally extended on both wings.

6. A large cable, perhaps a broken power or telephone line, is lying on the ground.

The investigation has only just begun, and discussion from here on may not apply directly to the New Milford crash. As always, this event merely serves as a reminder of what might have happened, so we can consider those LESSONS and mitigate those risks every time we fly.

Five of my six observations are consistent with an impact during a developed spin. According to Air Safety Investigators (ASIs), there are six basic patterns of post-crash wreckage:

1. The hole in the ground 2. The spin impact 3. The spiraling impact 4. The small angle of impact 5. In-flight disintegration 6. The wire strike

From that same source: In the spin impact, the plane dives into the ground, usually at a nose-down attitude, while spinning. Because of the relatively low speed associated with spins, the crater produced is shallower than the hole-in-the-ground pattern. The wings will have scarred the ground outside the impact crater. The inside wing of the spinning aircraft is usually the first to strike the ground, with the outside wing creating a ground scar directly opposite the scar produced by the inside wing [assuming a low-wing airplane where both wings impact the surface—TT]. The scars on the ground will indicate the direction of rotation. While most airplane crashes impacting in spin-type accidents do nose down, occasionally some will impact flat.

Further, other sources (and my Masters-level Air Crash Investigation course notes from what was then Central Missouri State University) tell us:

…it’s possible sometimes to determine the direction of the spin rotation by airframe deformation.

Specifically, the left wing appears to have impacted first. When the airplane’s rotation suddenly stopped, inertia caused the empennage to bend in the opposite direction as the tail rotated slightly longer than the main mass of the airplane. I’m certain that investigators will strongly suspect the airplane was spinning when it hit as a result of viewing the wreckage.

See: http://aibolita.com/sundries/11843-crash-patterns.html http://www.dviaviation.com/wreckage-analysis.html https://www.ucmo.edu/aviation/grad/ Because the airplane appears to have been in a fully developed spin on impact, I suspect the broken wire was not related to the crash—the airplane had to have departed controlled flight while high enough to enter a full spin. The airplane may have hit the wire during a spinning descent. The broken cable is the one of my six observations that does not seem to fit the others.

Of course, investigation may well determine I’m completely wrong. That’s why we have expert ASIs and not just Internet lurkers like me.


We do know that the pilot and instructor were attempting to take off from a short grass airstrip with obstacles at least on one end, as seen in the picture above, according to the news report. Partially extended flaps are consistent with an attempt a short- and/or soft-field takeoff, using standard Cessna 172 technique. See http://www.newstimes.com/local/article/Reported-plane-crash-in-New-Milford-11750399.php#photo-13685275 So where am I going with all this? What does this event suggest—even if later investigation determines some other cause—that we need to consider on all takeoffs? Why do I say this is a scenario for which we almost never train? The photos from the crash that prompts these thoughts suggests to me a power on stall during an attempted short-field takeoff, that developed into a spin.

With the additional weight of an adult passenger in the rear seat, an airplane will tend to pitch upward to a higher angle of attack than “normal” as the pilot attempts an obstacle-avoidance takeoff. For a given amount of physical pull on the controls (the result of “muscle memory” from more training-weight short-field practice), the airplane will tend to attain a higher-than-normal angle of attack.

The addition of flaps means the optimal climb attitude may occur at a lower-than-expected airplane pitch attitude…the “sight picture” out the windscreen may look normal when the airplane is at a dangerously high angle of attack.

We almost never train short-field takeoffs at airports that actually have short runways, or that have real-world obstacles that dare us to pull the nose just a little bit higher to get over the hazard when pushing down is the right thing to do. Stalls tend to be more dynamic (i.e., nastier) when the rate of deceleration is greater than the recommended one-knot-per-second rate of practice stall deceleration—resulting, perhaps, from an aggressive pull (conscious or not) when obstacles are closer than you’d like, and getting larger in the windscreen.

We almost never practice maximum-performance takeoffs at high airplane weights, or with weight distributed toward a rear-loaded condition.

We almost never practice power-on stalls in anything other than a clean airplane configuration, with flaps up and (in retractable gear airplanes) with the landing gear up. A draggier airplane decelerates more rapidly, approaching a stall faster than we see in common practice sessions. Stalls with flaps extended are usually more dynamic than clean-airplane stalls (maybe this is why the FAA suggests power on stalls be done “clean”).

We almost never see these factors combined to create the onset of a stall at a pitch attitude where we might still have the obstacle ahead of us in sight.

With very good reason, we never do all this close to the ground, where every nerve in our body would tell us to pull up instead of PUSH down and HOLD to keep flying and avoid impact. See http://www.flightsafetyaustralia.com/2016/07/push-and-hold/

It’s hard to visualize stalling on takeoff, in large part (I believe) because of the way we are taught and evaluated on power-on stalls. We’re told an airplane can stall at any speed, and any attitude. But the way we train and evaluate power on stalls to meet FAA completion standards, it’s constantly reinforced in practice that the airplane has to be pointed extremely nose-high to get it to stall with the power at full. And even then, we have to work at it to make most airplanes attain a power-on stall, at least at typical training weights and configurations.

The FAA manuals’ diagrams (and similar ones in other countries) reinforce this as well. The standard diagram shows that most general aviation wings stall at about 17°: the critical angle of attack. The usual depiction of critical angle of attack looks like this:


It may not be intentional, but it sure looks like the nose of the airplane must be pointed way up to attain a stall…at least in the standard diagram.

The wing’s chordline, however, is usually not aligned with the longitudinal axis of the airframe. The wing’s angle of incidence is such that the wing has a fairly positive angle of attack even when the airplane is sitting on the ground. This helps the wing generate lift during the takeoff ground roll. The angle of incidence (sometimes also called the fuselage mounting angle) is often designed to give the airplane a fairly level pitch attitude at a cruise-flight angle of attack. In most general aviation airplanes the angle of incidence/fuselage mounting angle is about 6°.

And the airplane’s direction of flight is rarely the same as the direction it’s pointed. In fact, an easy definition of angle of attack is the difference between the direction the airplane is pointed and the direction its wing is going.

I used my awesome PowerPoint skills to take that same diagram and alter it to show the takeoff stall scenario. I drew a simple airplane around that wing diagram, like this:

Visualize the airplane lifting off and beginning its climb. The nose is up…but the airplane is still moving forward across the ground. There’s a big difference between the direction the airplane is pointed and the direction its wing is going.

If the critical angle of attack is 17°, and the angle of incidence is 6°, then the wing may begin to stall at as little as around 11° airplane pitch attitude—about a normal VX climb attitude! Now, the angle of attack for a given pitch attitude will be lower with more power, so the airplane does not stall if you raise the nose one degree from the VX attitude…but you’re still close.


The LESSON is that maximum performance takeoffs are an exercise in extreme precision. When the airplane is heavier, or the center of gravity is more rearward, than you’re used to, you have to be even more precise with pitch attitude to attain the maximum performance…which is very close to the stall.

Need more convincing? When we talk about stalls, we usually talk about the base-to-final-turn, power-off stall in the landing configuration. We almost never talk about power-on stalls in

the takeoff configuration. Yet a study released by the AOPA Air Safety Institute at Oshkosh last month, Stalls and Spin Accidents: Keep the Wing Flying, tells us that:

The highest proportion of stall accidents on personal flights actually occurred during takeoff and initial climb. These made up 26 percent of all and 22 percent of fatal stall accidents. Accidents during landings and go-arounds, on the other hand, were relatively less common at 10 and nine percent, respectively. Deaths resulted from almost 40 percent of the takeoff and 30 percent of the go-around accidents but less than 10 percent of those during landing attempts.

See https://www.aopa.org/-/media/files/aopa/home/pilot-resources/safety-and-proficiency/accident-analysis/special-reports/stall_spin.pdf?la=en

A chart in the ASI’s study reveals the rate of traffic pattern stalls by phase of the pattern, both total stalls and fatal stall events. It’s probably not what most pilots would expect.

The AOPA ASI study, by the way, echoes the conclusions I found a few years ago when researching what I came to call “The Truth About Stalls”—that we have far more power on departure and go-around stall crashes than we do base-to-final or final approach stalls. True, some of the takeoff and climb stalls followed a loss of engine power. But far from all of them. And it’s still the pilot’s job to PUSH and HOLD for airplane control, when a power loss occurs. See http://slideplayer.com/slide/1374231/

Yet, we usually do not experience what a takeoff stall looks like until we are faced with one “for real”, usually at a heavy weight or more rearward-than-normal center of gravity condition, often combined with moderate to high density altitudes.

We can’t practice power-on stalls close to the ground. But we can practice power on, takeoff configuration stalls at altitude, even though the Airplane Flying Handbook and FAA Practical Test technique calls for power-on stalls in a clean (flaps and gear up) configuration.

We can ballast the rear seats or baggage area, remaining within the approved envelope, to experience power on stalls in the configuration that is historically most likely to occur. I highly recommend you explore this with an instructor on board, one who is very familiar with the stall characteristics of your specific model of aircraft. Ironically, this may have been one motivation for the Cessna 172 PRI and CFI to carry the rear seat passenger, in the fatal event that sparked this discussion.

Lastly, any real-world short field takeoff should be preceded with very recent practice in the technique at an airport with a greater margin for error. It takes extreme precision with pitch attitude, airspeed and angle of attack to fly a maximum performance takeoff without reaching or exceeding the critical angle of attack. You must be practiced and ready before making the actual attempt.


Comments? Questions? Let us learn from you, at [email protected]

See http://www.pilotworkshop.com/info/getting-started-with-flight-simulation-sale/

Debrief: Readers write about recent FLYING LESSONS:

Frequent Debreifer David Dewhurst writes about last week’s LESSON:

The Incident involving Air Canada 759 at SFO could happen to any of us. Not that I have ever turned final for the wrong runway, but I understand other people have done that. Uh, OK, we will go with that.

[My instructors and I] teach pilots to load the approach for the intended runway even in visual conditions. First, ATC may ask us to go direct to the final approach fix for the visual approach. The FAF is already in the flight plan so going direct is easy. That also puts us on a five mile final for the correct runway. Second, it is good situational awareness for where the final approach course is located. For airports with lots of runways built back when concrete was cheap, this is a real help. The third reason for loading the approach is that following the navigational information assures the pilot is on final for the correct runway. Had AC759 made that simple move the problem could have been avoided.

It indeed “could happen to any of us.” That phrase, so true here, is probably the biggest reason to read (and for me to write) FLYING LESSONS Weekly. There are many ways to reduce risk. Even when we think the level of risk is low, there is usually something you can and should do to reduce it even further. Thanks as always, David.

Comments? Questions? Let us learn from you, at [email protected].

Best info that I receive about flight safety! - Brian P Conway

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Oops

Several readers reminded me that Harrison Ford’s taxiway landing, a discussion point in last week’s LESSONS, took place at John Wayne/Orange County, California, not Santa Monica. KSMA was the site of Ford’s earlier mechanical engine failure in a Ryan PT-22 (an event he appears to have handled quite well, and which highlights the importance of proper maintenance and shoulder harness installation). The location of the taxiway landing is not important to last week’s discussion, and I hope my error does not detract from the overall LESSON to go around early if something doesn’t seem quite right on final approach. Thanks, readers, for letting me see my mistake and make this correction. See: http://www.mastery-flight-training.com/20170810-flying-lessons.pdf https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20150305X93207&AKey=1&RType=Final&IType=FA


Share safer skies. Forward FLYING LESSONS to a friend

Pursue Mastery of Flight.

Thomas P. Turner, M.S. Aviation Safety Flight Instructor Hall of Fame 2015 Inductee 2010 National FAA Safety Team Representative of the Year 2008 FAA Central Region CFI of the Year Three-time Master CFI

FLYING LESSONS is ©2017 Mastery Flight Training, Inc. For more information see www.mastery-flight-training.com, or contact [email protected].

2017.0817 flying lessons · 17-08-2017 · to air safety investigators (asis), there are six basic...

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