Charlotte Richardson - danlj

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Photo byCharlotte Richardson

BY DR. DANIEL L.JOHNSON

Aerobatics - Dangerous?Clearly, at some point someone had to

teach themselves aerobatics, but in those dis-tant days - when aviation was bright andnew - a high fatality rate was quite roman-tic. Not any longer.

- British Gliding Association Instruc-tor Manual, 2011

recent, thought-provoking notefrom a CFIG asked (paraphrasing

to keep the issue general), "While over-seas, I was very active in glider aerobatics.Now that I'm back in the U.S., I would like

to teach aerobatics. However, my club rulesspecifically prohibit acrobatic maneuvers.There are several issues being cheerfully de-bated, including, Who should not do high-Gmaneuvers?"

Right at the top, we must say that acr-obatic flight, when performed properly,should be safe as well as exciting. At thesame time, this monthly essay is dedicat-ed to the principle that intelligent, edu-cated, responsible, well-trained peoplesometimes are seen doing things thatappear incredibly dumb. Some of which

get us killed. So we should review this.It's important to discern the difference

between risk and danger. Normally, weuse "risk" to describe a decision weighedin view of known hazards and impor-tance or benefit. We tend to use "danger"to describe factors of risk that are out ofour control or are somewhat unpredict-able - or that are present. The waterfallnearby is a danger; risk is related to howclose we walk, how slippery is the ground,how strong the wind, whether we crossthe railing, and so on.

Risk may be managed; danger avoided.My judgment is that the dangers of

aerobatics are analogous. It is obviouslypossible to fly all types of acrobatic ma-neuvers safely. However, there are manyrisks, the greatest of which lie in ourselves:complacency, indiscipline, inadequatetraining, and lack of careful practice.

I reviewed many fatal aerobatics crash-es, and thought about all the many com-ponents of risk. G-loads get most of the

www.ssa.org • September 2014 • Soaring

press, but many other factors are moreimportant. Just a month before thiscolumn was written, a local friend, animportant cog in our airport's life, diedgiving an air-show performance. WhileG-forces may have been a contributingfactor (he did a sharp pullout from adive into a zoom), he had performed thismany times, knew what to do, and lostcontrol in less time than the 5-6 secondsof positive G that are cited as requiredfor loss of consciousness.

In his accident, he unintentionallysnap-rolled just as he began the zoom- watching the video, it seems obviousthat he pulled hard, induced an acceler-ated stall, and lost control. As his mentorand show partner remarked later, "Thenit doesn't take much to snap it." A smallburble of thermal turbulence causingdifferential flow across the wings, a lightpush on a rudder pedal, etc.

A search of the NTSB accident data-base shows that every year brings severalacrobatic accidents, mostly at air shows,with several fatalities. Yet most acrobatictraining and performances are complet-

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ed without incident, so success is expect-ed, leading to an air of surprise in thecomments of accident witnesses.

... acrobatic flight,when performed

properly, should besafe as well as exciting.

What could go wrong?Let's keep this simple: There are only

three candidates:

1. Turbulence.The air is invisible. Air shows are

mostly on sunny afternoons, when ther-mal activity is maximal. Acrobatic prac-tice is least expensive, in gliders, whenthermals permit cheap altitude recovery.

One day, a crop-duster pilot came intomy office with a snapshot of a huge ballof bent metal tubing lying in a bean field."What is that?" I asked.

"My helicopter," he said."What happened?""I flew into a dust devil." He was

somewhat bruised, and lucky to be alive.Some acrobatic maneuvers involve ap-

proaching a stall. Near a stall, small dif-ferences in relative airspeed between thetwo wings may spin or invert the aircraft.Sufficient windspeed differences areconsistently present in any self-respect-ing thermal or wind-shear turbulence.I would guess that this is an importantreason, when the air is bumpy, not to doacrobatic maneuvers near the deck thatmay involve a stall or accelerated stall.

It's impossible to know how muchinvisible atmospheric burbles have con-tributed to each year's list of acrobaticcrashes, but I cannot believe it's zero.

2. The aircraft.The Czech aircraft manufacturer, Let

Kunovice, took the Blanik L-13 outof the air in June, 2010, after a metal-fatigue acrobatic accident. In March,2013, a Schleicher Ka7 broke a wing,and the pilot and a young boy were killed(NTSB case CEN13FA213).

Years ago, in my state, a renowned andbeloved acrobatic instructor and his stu-

dent were killed doing a loop when thewooden spar of his old Citabria brokedue to undiscovered dry rot.

A friend lost his airshow partner whenon a season's first flight the elevatorhinge, which had acquired new corro-sion during the winter, became jammedin the up-elevator position on takeoff.

I'm sure that most of my readers canmake their own lists of similar incidents.

Aircraft qualification.It should be obvious, but apparently

is not (given the Ka7 accident above),that aircraft not certified for acrobaticflight should not be flown acrobatically.(Me!? Read the manual!? Loops androlls don't stress the airframe!)

Aircraft Inspection.There are obviously three key tasks we

face regarding the safety of the airframe.A. The unknown:

• Detection of previous over-stress to airframe. (Do we knowwhether placid, trustworthy fellowpilot Walter Mitty has been play-ing for thrills when alone in thesky?)

• Detection of airframe or con-trols deterioration. (Rust, fraying,dry rot, corrosion, etc.)

B. The known: Inspection for possibleoverstress requires a g-meter, I think, tobe aware it's happened.

C. The design: What uses, and whatstresses is the aircraft designed for?

Has the aircraft had a properly annual?I am all too familiar with the cursory

annual, followed by an either an incidentor by a careful annual at which long-standing materials defects are discovered.(There is another type of bad annual, inwhich many false issues are discoveredand remedied for the income gener-ated, a standing policy at some FBOsI've known.) We all can tell stories aboutboth bad flavors.

What is needed is an inspection by anAI who is familiar with the model andknows something about its design andabout aircraft-materials engineering. It'sworth the expense.

3. The pilot.Pilots are not invisible, and we don't

actually rust. Our failure modes are

Soaring • September 2014 • www.ssa.org

much more complex. Tom KnaufP's let-ter in the March, 2014, issue of Soaring,Developing Discipline, eloquently de-scribed this central key to safety. We aresafest when we meticulously fly withinwell-understood boundaries. Obsessivecompulsiveness is a healthy feature ofairmen who survive to old age. It's a dis-order only when it hinders function!

I've twice worked with a little gliderclub. One consistency has been that everytime an operational detail was skipped,there was a related risk of an incident.Pertinent to this, every incident I canrecall has entailed missing one or morepoints. Whether we call the necessarymeticulous attention to detail disciplineor perfectionism or caution, each flightcan be thought of as a (sometimes rapid-fire) sequence of items, requiring eitherattention or action, none of which can beignored without risk.

What are the features of safety in glideraerobatics?

Our organizations.Our clubs and associations do take

responsibility for enhancing safety. Or-ganizations can only function throughrules and procedures. These define ex-pectations. The easy way to limit autoaccidents is to take away the keys. Wedo this, in clubs, regarding aerobat-ics, because the occasional foolish pilotdoes exist, and because higher-risk flightmodes require careful preparation ofaircraft and pilots that are often beyondclub resources.

Insurance companies have long ex-perience with rogue pilots performingaerobatics, often causing big payouts.They are in business to compensate forloss, but they will not stay in businessunless losses are limited to a numbercomfortably less than premiums minusoperating expenses. The policy your clubhas signed may have taken away thekeys. Read your policy before you startan acrobatic program.

TrainingWe are not going to give tips today

on proper acrobatic training. For onething, this is outside our arena of com-petence (though that doesn't always keepus quiet). The salient point here is that

proper training is the most importantfeature of safety, and training requiresproper, diligent, frequent practice. We'renot "done" at signofT, we've begun.

RulesMost rules in aviation, as in medicine,

are written in blood. This is worth re-membering when we chafe at a rule thatseems ill-considered. It's important toask ourselves, "Why might this rule havebeen created?" Yes, there are dumb rules(not well thought out), but rules are writ-ten to reduce risk.

The intent of most rules is pretty ob-vious. Understanding the intent of therule allows us to go beyond the rule inreducing risk by following the principleswhen they conflict with the precept. Theclear rules of acrobatic flight are not to bestretched: approved airspace, hard deck,acrobatic-certified glider, parachutes,proper preparation.

With acrobatic flight, we have manyregulatory and legal requirements re-garding all aspects of flight (e.g., harddeck, passengers, etc.) that are createdby every level of authority (club, airfield,government).

For example, if you want to do aerobat-ics near an airfield, you must file a formalrequest of the FAA to have a practicebox. This is an excellent idea - we createdone at our local airfield - because a goodrunway is close by if a quick landing isneeded. However, it does inconvenienceother traffic. For example, no instrumentapproaches or departures will be permit-ted by ATC during the hours that thepractice box is open.

But it's safer for many reasons, not theleast of which is that the aerobatics isdone in a well-advertised, clearly-com-municated area, which seems safer thandoing it over a pasture in a random direc-tion a few miles away.

Flight preparation and planningWeight and balance, and equipment

requirements, weather, traffic, etc., are ob-vious factors which, on reading accidentreports, are sometimes left aside. This iscomplacency and indiscipline. These arebases that have to be touched, if only toreflect on what may have changed sincelast we reviewed them thoroughly.

Aircraft preparation. What is on the

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floor and under the seats that will fly intoyour eyes and mouth when you go nega-tive. Should the cockpit be vacuumed?

Physiological factorsTwo things are uniquely important to

acrobatic flight, both related to the factthat no activity is safe unless our brainfunctions well.

The first of these is spatial orientation.Awareness of our position and velocity

in 3-dimensional space is crucial. Part oftraining involves learning techniques todo this during unusual attitudes. Main-taining spatial orientation is physiologi-cally complex. Not everyone has the sameability to do this. Our orientation sys-tems have limits and failure modes thatare well understood, and are describedin books of aviation physiology. Read up(see references, below).

The most interesting perceptual phe-nomenon of acrobatic flight is one called"the wobblies." After a flight involvingmany changes in orientation and g-load,the pilot may have trouble walking. Atorrent of perceptual data and the need toanalyze it rapidly has somehow created astate in which the pilot's system can nolonger function.

If you want to study this, searchfor "G-induced vestibular dysfunc-tion," cited at the foot. It is commonand not much discussed. The instabil-ity involved may last for weeks (duringwhich the pilot should stand down),though usually for a few hours. It iscommonest after pulling more than-4Gs (not much done in gliders, eh?)or when pulling +Gs after a negative-Gmaneuver. It usually includes vertigo (anauseating sense of rotation).

The wobblies are more common if any-thing is wrong with the middle ear orthe spatial-orientation system: allergy,colds, medications, aging changes, spinaldisease, etc.

The second important physical factor isG-tolerance.

As you know, all perception, planning,and action occur in the brain, which doesnot function without a steady inflow ofglucose and oxygen. This depends on apump and resilient, complex plumbing.

A pump requires some inflow pressure,good valves, and a strong motor to pushblood flow against resistance.

We have a G-tolerance detector, vision.The retina - part of the brain, actually - ishighly active metabolically, so any loss ofglucose/oxygen/pressure instantly reduc-es vision. Tunnel vision and grey-out aresigns that we're on the edge of the G cliff.

Limits of G tolerance.There's a lot of variation, between in-

dividuals and between situations, in whatG forces can be managed. Brief exposuresto what are essentially hard knocks ( + 12,-10 G) can be managed with training.Untrained individuals in adverse situa-tions may be incapacitated by +2 or -1 G(yes, this cou/dbe you, on the wrong day).

Read Human Response to Acceleration(cited at foot) if you want to learn thefine points.

First, the standard work on G tolerancewas done with young, healthy, fit males,during WWII, in a centrifuge. This cre-ates a useful guide, but doesn't apply pre-cisely outside those conditions.

Awareness of ourposition and velocity

in 3-dimensional spaceis crucial.

An important factor is the push-pulleffect.

Negative G causes the heart to slow,veins and arteries to dilate, and dimin-ishes the strength of the heart muscle'scontraction. This decreases the heart's ca-pacity to pump high volumes of blood tothe brain.

This has some momentum of its own,and does not revert just because youdecide to roll from an outside loop to in-side. Recovery can take at least 8-10 sec-onds, depending on magnitude and dura-tion of negative G. This causes very lowblood pressure when transitioning fromnegative to positive G, greatly reducingtolerance.

The brain can function for 4-6 secondswithout good blood flow. Pilots can typi-cally endure -2 to -3 G, and +3 to +4 G,but when the pilot goes back and forthbetween only -1.0 G and +2.25 G, theblood pressure may fall to zero when G

changes from negative to positive. Thisaffects perception and performance atbest, and loss of consciousness at worst.

Medication versus G-forceMany pilots take medication of various

types. Some of these are prescribed toreduce blood pressure, a scourge of west-ern society. Others affect blood pressureas a side effect. For example, the drugsprescribed to men to improve flow or toincrease the turgidity of the faucet areactually blood-pressure medications.

Diuretics not only reduce blood pres-sure, but also reduce blood volume, asdoes dehydration, whether from sweat-ing, diarrhea, vomiting, or simply failureto drink adequately.

A useful way to use the Internet to ex-plore your own medications is to searchfor "postural hypotension" preceded (oneat a time) by the name of each medica-tion. You'll get a lot of hits, but if yourmedication isn't named in the first pagedisplayed, don't bother reading further.

If any medication is sometimes a causeof postural hypotension, your G-toler-ance will be reduced. I personally wouldnot do anything more strenuous than awingover or a stall if on diuretics or med-ications affecting blood pressure.

Disease and DeteriorationMost pilots are beyond our youthful

bloom. Years ago, when I first started pre-senting on the effects of aging in pilots,many studies were sponsored by the mili-tary, where over 40 is rather elderly. In our40s, the slight loss of physical capacity isovershadowed by experience. However,over 70 is very definitely elderly (physi-ologically), and in case you haven't no-ticed personally, the resilient parts havebecome stiff and the elastic parts floppy.This reduces G tolerance.

A normal health condition for somepilots is pregnancy. The most impor-tant changes in blood volume and bloodpressure occur during the third trimes-ter. I think that good rules of thumb arethat if you don't look pregnant and arecomfortable, the pregnancy isn't yet arisk; if you are starting to feel big, it is arisk for reduced G tolerance. Ultimately,the uterus takes 20% of blood flow andwill pop fatally if whacked, such as bybig G forces.

Soaring • September 2014 • www.ssa.org

The commonest diseases of the elderly in the West are car-diovascular disease and diabetes. Both the diseases and theirtreatment cause cardiovascular and blood-volume changes thatdecrease G tolerance in several ways.

Heart disease affects the strength and competence of thepump itself. Atherosclerosis decreases the resilience of arteriesand may cause significant unsuspected strictures, including thearteries to and within the brain.

The brain itself shrinks with age, making it more liable toflop around within the skull, creating risk for brain injury andconcussion from jerks and whaps.

The Wrong StuffEven when we are healthy, not all of us have the physical

gifts that permit safe acrobatic flight. Some of us are betteroff to realize that we have the wrong stuff for it, and are betterspectators than participants at the sport. This is a hard self-assessment, yet an important one. We are all different from oneanother.

Responsibility and JudgmentNot everyone has the same ability to exercise judgment. This

ability is not inborn, but is learned through our upbringingand formative experiences. We do not show better judgmentwhen playing in airplanes than in our social or work life.

A person's attitude toward rules, and whether their rule-breaking is considered or impulsive, is important in judgingwhether we can trust them to be prudent when out of sight.

A person who habitually takes others' concerns seriouslyis generally someone we can trust to respect equipment andprocedures.

A person who comes to the field prepared and doesn't skipover details is also someone who can be trusted to take care oftraining details and practice for aerobatics.

A person who seems cranky and fussy, though often annoy-ing, is characteristically someone who can be trusted with de-tails, if not with club diplomacy. Contrariwise, the gregariousand convivial club member, full of enthusiasm and optimism,is not typically the sort of detail-driven person who does wellin charge of an operation.

SummaryWe've taken a broad view of the risks that may be associ-

ated with aerobatics, which go far beyond G-tolerance, andthe human-factors risks are more behavioral than physiolog-ic, something that is normally less thought about. Obviously,most such risks are not at all unique to acrobatic flight, andneed to be part of our checklist in creating such an operation.

My point is not to discourage you from learning and per-forming aerobatics - unless you think that the checklist thiscolumn represents is unimportant. Every detail counts.

ReferencesDarker Shades of Blue: The Rogue Pilot. Tony T. Kern,

2006. Pygmybooks.comA careful study of the characteristics of pilots who repeatedly

cross the boundaries.

G-induced vestibular dysfunction ("the wobblies") amongacrobatic pilots: A case report and review. Muller TU. ENT-Ear, Nose, & Throat Journal, V81, No4, April, 2002, p. 269-272.A very insightful discussion by the US Aerobatics Team physi-cian, who understands both the sport and the physiology.

Gliding International, May-June 2014, p 59, NTSB Acci-dent Report Out on Glider Fatal - Probable Cause DeterioratingGlue Joints in the Wings. (And in a glider unapproved for aero-batics.) A sad story of poor judgment.

Human Response to Acceleration. Banks RD, BrinkleyJW, RR and Harding RM, Chapter 4 in Fundamentals ofAerospace Medicine, 4 Edition, ed. DeHart RL, Davis JR,Stepanek J, Fogarty JA. Williams 8c Wilkins, 2008. The bestcurrent summary of G-tolerance.

Spatial Orientation in Flight. Parmet AJ & Ercoline WR,Chapter 6 in Fundamentals of Aerospace Medicine, 4tn Edition,ed. DeHart RL, Davis JR, Stepanek J, Fogarty JA. Williams ScWilkins, 2008.

AcknowledgementsThanks to Terry Pitts for unintentionally triggering this

essay, and for the quotation at its head.In memory of Bill Cowden, a dynamic, talented, and skilled

man.

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