Eye of the Beholder

The question of instability and its solution depends on point of view


At the risk of falling into the category of the uninformed, I would like to comment on Graveyard Spirals [Reality Check, May].

The flight tests of an airplanes stability is broken into categories of static, dynamic and maneuvering. Control forces and the airplanes response to various test conditions are measured against the FAAs requirements. These are done with the basic requirement that the airplane should tend to return to trim condition exepect that the airplane is not expected to roll wings level when measuring stick force per g in maneuvering flight.

The tests of the phugoid mode, the spiral mode and the lateral-directional stability are done hands-off. The object is to determine if there are any oscillations of a short period that the pilot would have difficulty controlling. Where the period of oscillation is long, as in a spiral, it is assumed that the pilot can easily control the airplane provided he is aware of the motion of the airplane.

A driver cant take his eyes off the road or hands off the wheel for more than a few seconds, yet in the three-dimensional world of flight the pilots perception of any divergence is not so obvious.

All that leads to the question of whether the 85-year-old attitude indicator design is in need of an upgrade.

Is it a fault of the aircraft with its slowly divergent mode, or do we not provide pilots with adequate equipment for this well understood flight condition? Do we learn from experience or continue to resist new rules and aircraft equipment?

We thought we could explain and train pilots to control the lateral-directional mode in the big airplanes, but no way! The yaw damper was required. Explaining and training are not good remedies for poor design.

I agree that ignorance is an important factor, but I would say its not the ignorant pilot but the ignorant designer we should spend some time with.

-Jim Gannett
Redmond, Wash.

Volumes have been written about the phenomenon, but we like your attitude of accepting what is and trying to find a better route to safety. Relying on current attitude indicator design seems a bit like choosing an NDB approach and turning off the moving map GPS.


You Say Unstable, I Say Trimmed
I couldnt believe that Donnal Smith, given his aviation education and experience, would write an article on Graveyard Spirals that completely confounded the topic [Reality Check, May].

Through this article, Aviation Safety has done a disservice to its readers, particularly those less experienced VFR general aviation pilots.

A graveyard spiral has nothing to do with aerodynamic instability. Stability refers to a trimmed condition, not straight and level flight. Do not confuse flight path with stability. The airplane is stable if given a small perturbation it returns to its trimmed condition. The airplane will likely oscillate but the oscillations will dampen out.

To say most general aviation airplanes are inherently unstable is incorrect. General aviation aircraft would never be certified if they were truly unstable. Only recently have certain military aircraft been designed with certain amounts of instability. A spiral is a stable trimmed condition; it is nothing more than a continuous turning descent. An undesirable flight path does not constitute instability.

IFR rated pilots have been trained to recognize and recover from spatial disorientation. VFR pilots are more susceptible, if they should enter IMC. However, this is a problem for all pilots. Periodic ground and flight training can help prevent spatial disorientation from becoming a disaster. In the future, I hope the editorial staff and contributing authors will more thoroughly research, then publish, accurate and informative articles.

-Alvin Brunner
Via e-mail

Mr. Smith replies: I believe you have completely missed the point and purpose of the article. You seem to be arguing that my use of the word stability is incorrect, and you apparently believe the graveyard spiral is a result of spatial disorientation followed by an inadvertent turn.

In addition, you say my statement that most general aviation airplanes are inherently unstable is wrong because general aviation aircraft would never be certified if they were truly unstable. The section of FAR Part 23 dealing with lateral stability has no requirement for an airplane to roll itself level when a wing goes down in straight and level flight.

The main idea of the article is to destroy that misconception.

In Aerodynamics for Naval Aviators, author H. H. Hurt describes the spiral tendency as mild and weak. In spite of the weakness, most airplanes will drop a wing and enter a spiral without any pilot input or disorientation, regardless of fuel load, turbulence, or any other factor. Call it whatever you want, but when the bank and dive angles increase and the airspeed rises toward the red line, I prefer to think of it as instability.

The belief in total stability held by most pilots is hard to destroy. I am not an aerodynamics engineer, and these are not my ideas. The authoritative texts mentioned in the article back up everything I said.


Youre Scared? Good
I am a full-time CFI at a technical college in Wisconsin. I came home from a trip today to find your cover story on the graveyard spiral [Reality Check, May].

For years now, one of my favorite unusual attitudes exercises has been to simply let the airplane go. If the spiral doesnt develop fast enough, I add a tiny bit of rudder. After the student has recovered, I show him or her what I did to get the airplane there. The fear of God enters their soul rather quickly.

I also have my students do slow flight and stalls at night over Lake Michigan, headed away from shore. I prefer a high overcast and/or no moon on the nights I take them up. Once again, the fear of God enters the soul…

-Dan Colburn
Via e-mail

The demonstration of the airplanes lack of stability is useful, but wed take issue with your use of fear as a motivational tool and your practice of combining stalls and black hole effect. Not that you asked us.


Can We Use Crib Sheets?
In his article Master, Slave or Partner [Airmanship, May] Ron Levy writes: All pilots in the Air Force must take a written test on the boldface emergencies for the aircraft they fly before their first flight each week. They are handed a paper listing the titles of all the boldface emergencies for their aircraft, and they must fill in the boldface steps for each one, exactly as they appear in the book. Passing requires a score of 100 percent, and if you dont pass, you dont fly.

Wow, maybe the Air Force has gotten a lot more picky since my five years of service. Sure, we had to know the boldface emergencies, but they never handed us a piece of paper on a weekly basis. It seems unlikely. How could we stay combat ready if we had to take time out for weekly written tests?

Is this a recent requirement? Where did Mr. Levy get his information?

-Gil Buettner
Via e-mail

Mr. Levy replies: Since there arent that many emergencies or boldface steps per emergency (for example, the F-111 has eight emergencies with 16 total steps), it took about three minutes to do. If it took longer, you didnt know it well enough. The hardest part for most was slowing the brain down to keep pace with the pen.

It was a requirement for the entire time I was a USAF fighter crewmember, from 1978 to 1988. However, because of your note, I rechecked with the Stan/Eval shop at HQ Air Combat Command, and found that the requirement has changed since then. The hand-written test is only required by regulation once a year, and the rest is up to the individual squadrons, some of which test more often.

However, crews must take a Situational Emergency Training check that covers the boldface emergencies before the first flight of each month.


Correct Response? Check
I enjoyed very much the article on checklist usage [Airmanship, May]. There seems to be an overemphasis on the checklist these days. Too often it becomes a do list rather than a checklist. We must remember that it is a checklist, and that means do the items either by memory or flow, and then use the checklist to be sure you have accomplished all the items.

I am a pilot for a major airline, and a few years ago the FAA came down on us for checklist usage. Well, in typical FAA fashion they said that we must answer the challenge part of the checklist with the exact response called for. This led to so many of us wanting to be sure that we responded properly, that the item be checked was completely ignored. So much for safety.

We have to keep in mind that the reason we use a checklist is to be sure the critical items are done prior to a critical phase of flight. We cannot let running a checklist take priority over flying the airplane, or doing all the other things necessary for safe flying.

In flying my personal airplane, I use a flow pattern with emphasis on what I call the killer items: fuel, trim, flaps, flight controls free, door closed, landing gear down. These are the things that will hurt you, and some of the other things are less important, because if they are forgotten or missed they will not kill you or cause damage to the airplane.

-David Bradshaw
Weatherford, Texas

We cant fault your logic, but would like to point out that some pilots feel just as strongly about the need to use checklists. The important thing is that the pilot should be thinking about whats going on rather than doing it by rote, whether using a printed checklist or a flow check.


Touch-and-Goes Hurt Go-Arounds
In response to the article on go-arounds [Proficiency, May], we believe the emphasis on touch-and-goes in flight training cements poor go-around habits. If you perform 100 touch-and-goes and then must do a go around, the chances are good you will use your touch-and-go technique.

Pilots who perform touch-and-goes also develop the bad habit of letting the nose gear drop to the pavement prematurely. They do not learn the important technique of holding the nose gear off the runway until it comes down by itself. Touch-and-goes are also poor ways to learn the proper use of flight controls when there is a crosswind.

We now do all full-stop landings at our flight school, which operates 30 aircraft flying more than 12,000 hours a year, and produce a better and safer pilot.

If you must do touch-and-goes, let the plane slow to about 10 mph prior to the go and use the go-around technique.

-Louis Mancuso
Islip, N.Y.

Ask any student pilot the value of touch-and-goes, and youll hear that its the cheapest way to get 12 landings in. Although we agree with your conviction that T&Gs lead to some bad habits, economic reality has cemented their place.

Licensed pilots going up for their weekend practice, however, should take note and remember that the flight isnt over when the wheels touch the ground. Takeoff and landing roll procedures need practice, too.


Angels, Ghosts and Other Lessons
Concerning When Time Runs Out [Learning Experiences, May], is Aviation Safety to become a place to flaunt our spiritual connections? This publication has been a great source of aviation learning, but if your staff is willing to give audience to writers emotional comments and religious anecdotes, like those that blossom forth from this article, you are threatening the serious discussion of safety.

Cant you ask the submitter to edit his personal asides before you publish them? Maybe I should write an article and make comments about people who rely on spiritual beings to do their learning for them and save them from harm. Some pilots have a little prayer before they start up the engines or call ready for takeoff. This might give them confidence to overcome the emotions the writer mentions, but how much safer they really are is a subject far removed from what Aviation

Safety has been all about.

Start a publication called Angels In The Airways, where everybody who believes can write in about how their favorite deity saved their tails after they made a big pilot error. How about the ghosts who were taken to heaven by the angels when they forgot to buy fuel? Lets hear from them.

No doubt you will edit this letter carefully.

-John Miller
Greensboro, N.C.

Religious connotations aside, we hope the writers compassion for the family of the dead pilot inspires every pilot to recognize the risk involved in flight. For that reason, it is commendable and very worthy of print. Your letter, by the way, is edited as little as the rules of grammar allow.


Flight Hours Are Just Part of the Job
Flight instructor pay [Editors Log, April] is an issue that definitely needs to be addressed. One thing I would like to add is that many flight instructors dedicate a great many hours reading, studying, preparing lessons and so on, which is what makes them good instructors in the first place.

I am a CFII, and in addition to my full-time career in the software industry, I spend an average of at least two hours per day reading and studying aviation and flight instruction topics. This is in addition to the time I spend each week actively instructing. The pilots with whom I fly appreciate this extra effort and are willing to compensate me fairly for it.

-Judy Cadmus
Collegeville, Pa.


Fix Your Broken Calculator
Im trying to follow Bruce Chiens article Go To Nearest [Instrument Check, March]. In discussing best glide in an M20J, he makes the statement, a nautical mile is about 6,300 feet. Since when? I thought it might be a typo, but I performed the math he describes and came out with his estimated 19-mile glide using 6,300 feet.

I may be wrong, but I learned and have always acknowledged 6,000 feet as a nautical mile.

This would generally be no big deal, but he performs so many calculations in this discussion that I think an accurate statement of some generally accepted assumptions is warranted.

-Mitch Markowitz
Via e-mail

Were afraid Mr. Chien gives 103.7 percent in all he does, and that includes math. For the record, a nautical mile is, in fact, 6,076.1 feet.


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