NTSB General Aviation Accident Prevention Symposium

September 21-22, 2000

NTSB Board Room
Washington, DC

Title: SPIN ACCIDENTS -- Comparing One Case with the Typical Stall/Spin Accident

Presenter: Rich Stowell, NAFI Master CFI

Copyright © 2000 by Rich Stowell

Abstract:

The net effect of fallible pilots flying imperfect airplanes at invisible angles of attack is significant. Close to thirty-three percent of stall accidents are fatal; sixty-six percent of spin accidents are fatal. Once encountered, the prospect for survival is bleak: one out of four aviation fatalities tied to a stall/spin, an 80 percent chance of serious or fatal injury, a greater than 90 percent chance that insufficient altitude exists in which to recover. This paper compares a specific stall/spin accident involving a Cessna 205 on a skydiving jump run (NTSB MIA97FA173) with the typical stall/spin accident model. The roles of the airplane, flight instructors, the pilot-in-command, and FAA in the stall/spin accident chain are discussed as well.

Discussion:

Stall/spin accident rates in general aviation have remained essentially constant since the late 1960's, continuing to account for roughly ten percent of all accidents, but twenty-five percent of fatal accidents. Some studies have suggested that these stall/spin accident rates are largely attributable not to improvements in pilot training, but rather to airplane designs introduced in large numbers in the late 1950's and throughout the 1960's. Flight lines today, in fact, still bear a striking resemblance to those of thirty years ago.

The stall/spin accident under review occurred on May 25, 1997 in Homestead, Florida. Catalogued as NTSB Accident Report MIA97FA173, the accident involved a 1963 Cessna Model 205 (C-205) being used as a parachute jump plane. The accident claimed the lives of the pilot and five skydivers. A sixth skydiver--positioned on the jump platform when the airplane entered the spin--bailed out without injury.

NTSB's final report cites the pilot-in-command's "failure to maintain airspeed" and "failure to apply spin recovery" procedures as probable accident causes. The report also cites "lack of training in spin recovery" and the "FAA's failure to require" spin recovery training in an aircraft as contributing factors.

The mission profile of the accident flight (i.e.: transporting skydivers) may seem inapplicable to flight activities normally involving light airplanes. Examination of this case, however, reveals just how closely it fits a typical stall/spin accident model. The listed "failure to maintain airspeed," for example, is cited as causal in nearly 90 percent of stall/spin accidents. A line-by-line comparison with a typical stall/spin accident is equally revealing:

The Role of the Airplane:

A study published by the Society of Automotive Engineers in 1976 ranked thirty-one airplane designs by combining their stall/spin accident rates using the formula: 10x(Fatal Rate) + (Total Rate). The five single-engine designs emerging with the "best" stall/spin accident records were all Cessna products. The Cessna 210 and 206--close relatives of the Cessna 205--were ranked fourth and fifth respectively.

The accident airplane was loaded within its approved weight and balance limits, albeit heavy with its center of gravity (c.g.) located aft of neutral. One pilot with more than 5,000 hours logged hauling skydivers and operating in the Alaskan bush in Cessna 205's and 206's opined that the 205 and early 206's lack sufficient elevator authority when heavy, slow, and loaded with an aft center of gravity. Later Cessna 206's were equipped with longer, more effective horizontal stabilizers/elevators.

For certification in the Normal Category, the Cessna 205 demonstrated recovery from a one-turn spin in not more than one additional turn. According to FAA Advisory Circular AC 23-1, Type Certification Spin Test Procedures issued in1964, this one-turn margin of safety was intended "to provide adequate controllability when recovery from a stall is delayed." Beyond the first turn in a spin, however, recovery cannot be guaranteed.

The Cessna 205 Pilot Operating Handbook (POH) states: "Should an inadvertent spin occur, standard light plane recovery techniques should be used." Such a superficial treatment of spins is typical in older handbooks. And what exactly are so-called standard light plane spin recovery actions? Advisory Circular 23-1 explains that "All spin recoveries should be made using the NASA spin recovery technique [consisting of] ailerons in neutral position, full opposite rudder to stop rotation, followed by forward elevator control as required...." During the 1960's at least, the NASA recovery procedure was understood to be the de facto standard for spin recovery.

AC 23-1 also states the following: "Evidence of an uncontrollable spin would be present if recovery cannot be effected within one additional turn by using normal NASA control recovery movement [emphasis added]." Yet Cessna 205 spin test documents show a non-standard use of ailerons while at the most rearward c.g. and maximum take off weight: "rapid application of anti spin control at one turn (rudder then elevator) and aileron against to confine recovery to less than one turn."

Notwithstanding the sheer lack of detailed spin recovery information available to the pilot, a conflict exists between the NASA standard spin recovery actions alluded to in the POH and the wholly non-standard use of aileron against to satisfy the one turn spin test requirement.

The Role of the Instructors:

The FAA implemented sweeping changes to stall/spin awareness training in April 1991. The pilot-in-command received his private and commercial flight instruction between January 1992 and June 1994. While I cannot comment on the specific stall/spin instruction the pilot received during that time frame, I can comment on the minimal stall/spin knowledge possessed by flight instructors in general.

In 1993, the Transportation Research Record published a flight-line study that assessed the stall/spin knowledge of general aviation flight instructors. Five hundred thirteen civilian flight instructors and twenty-eight designated flight examiners participated. The study quantified the lack of stall/spin expertise in our corps of FAA-certified flight instructors. For example, ninety-four percent of instructors relied primarily on popular literature (i.e.: aviation magazines) for their stall/spin information; ninety-six percent also relied heavily on their own instructors. Ninety-five percent of instructors failed ever to receive training in either spin dynamics or the likely conditions preceding an inadvertent spin. Ninety-four percent of instructors understood neither aircraft spin certification requirements, nor the operating limitations imposed as a result. Although instructors and examiners rated their understanding of stall/spin dynamics as "excellent," survey results clearly indicate that those charged with the task of teaching and testing new pilots possess a marginal understanding of stall/spin phenomena themselves.

Perhaps the most foreboding aspect of this study, however, involved the hands-on spin experience of flight instructors. Ninety-eight percent noted that their formal spin training consisted of no ground instruction and a mere two spins--one in each direction. Nonetheless, instructor applicants readily received logbook endorsements certifying that they were competent to teach spins.

The changes made to FAR Part 61 in 1991 attempted to improve stall/spin awareness across all levels of flight training, including the Flight Instructor Applicant level. Yet more than a year after implementation of the new stall/spin training standards, ninety-seven percent of the CFI's surveyed were still unaware of the regulatory changes. In fact, thirty-five of the instructors surveyed had been certified after the changes went into effect, yet not a single one of them was aware of the changes. Most instructors knew nothing about the FAA's well-written Advisory Circular AC 61-67B, Stall and Spin Awareness Training, published on May 17, 1991 either.

The Role of the Pilot-in-Command:

Eighty-three percent of general aviation flight time is spent in the climb, cruise, and descent phases. Yet only twenty-two percent of aviation accidents occur during these phases. By contrast, pilots spend a mere six percent of their flight time in the critical phases associated with the traffic pattern: takeoff, initial climb, approach, and landing. These phases, however, account for a dramatically disproportionate fifty-seven percent of aviation accidents (Aviation Instructor's Handbook, p. 9-12).

It's clear that every pilot should be devoting considerably more time to practicing the skills necessary to operate safely during the most critical phases of flight. The stall/spin accident under review was initiated at altitude during a skydiving jump run. Though not considered a critical phase in the traditional sense, the conditions of a jump run nonetheless emulate those associated with traffic pattern operations: low airspeed, high angle of attack, diminished control effectiveness, multiple distractions (increased wind noise, skydivers repositioning themselves, commands being issued by the jump spotter, etc.).

Logbook entries show that the pilot had 290 hours total time, with 82 hours in the Cessna 205. "Stalls" are specifically listed in the logbook Remarks section during flights totaling approximately 15 hours. The pilot logged stall practice in the accident airplane on one flight. Total time of this training flight: 30 minutes. It's not readily apparent if the airplane was loaded to simulate the weight and balance of a typical jump run during this short flight.

Based on logbook entries, I would estimate the actual time spent practicing stalls, stall recoveries, and likely stall/spin scenarios to be on the order of 3 hours--around 1 percent of the pilot's total flight time.

The Role of FAA:

As mentioned earlier, the FAA mandated stall/spin awareness training and published Advisory Circular 61-67B in 1991. The campaign to educate pilots about the importance of stall/spin awareness, however, has largely been ineffective. According to an informal survey taken during a number of safety seminars across the U.S. in 1998, only ten percent of pilots who had earned Private, Commercial, or Flight Instructor certificates after 1991 had also received a copy of AC 61-67B as part of their stall/spin awareness training package. Pilots who rely on either the FAA's Flight Training Handbook or the new Airplane Flying Handbook for spin information will find just 2-1/2 pages dedicated to this all-important and complex topic. And little guidance is provided regarding the spin training required of Flight Instructor Applicants. Consequently, pilots continue to be under-trained with respect to stall/spin dynamics and stall/spin accident scenarios.

Conclusion:

The net effect of fallible pilots flying imperfect airplanes at invisible angles of attack is significant. Close to thirty-three percent of stall accidents are fatal; sixty-six percent of spin accidents are fatal; forty percent of spiral accidents are fatal. Once encountered, the prospect for survival is bleak: one out of four aviation fatalities tied to a stall/spin, an 80 percent chance of serious or fatal injury, a greater than 90 percent chance that insufficient altitude exists in which to recover.

Accident prevention must be proactive if it's to be effective. As an industry, I challenge us to do a better job educating pilots about stall/spins. At a minimum, let's get AC 61-67B into the hands of students and instructors alike. Let's ensure that Flight Instructor Applicants are intimately familiar with AC 61-67B as well as the FAA's new video, Avoiding the Inadvertent Spin--which was recently released as part of the FAA's Safer Skies Agenda. Let's more strongly encourage pilots to practice slow flight and stalls on a regular basis. Let's demand more than one or two spin entries as sufficient for a Flight Instructor Applicant. And although I do not believe it would be feasible now to require spin training of all pilots, let's tirelessly encourage pilots to rise above the minimum acceptable training standards and to seek out spin training from qualified instructors as part of their continuing education.

References:

Bowman, James S., Jr. "Summary of Spin Technology as Related to Light General-Aviation Airplanes." NASA TN D-6575. Langley, VA: December 1971.

Diehl, Alan E. "Human Performance and Systems Safety Considerations in Aviation Mishaps." The International Journal of Aviation Psychology, vol. 1, no. 2, pp. 97-106.

FAA. "Aviation Instructor's Handbook." FAA-H-8083-9, US DOT, FAA, Flight Standards Service: 1999.

FAA. Hoffman, William C., and Walter M. Hollister. "General Aviation Pilot Stall Awareness Training Study." Report No. FAA-RD-77-26. Washington, DC: 1976.

FAA. "Stall and Spin Awareness Training." Advisory Circular 61-67B. Washington, DC: May 17, 1991.

FAA. "Type Certification Spin Test Procedures." Advisory Circular AC 23-1, April 1, 1964.

NTSB. "Special Study--General Aviation Stall/Spin Accidents, 1967-1969." NTSB -AAS-72-8. Washington, DC: 1972.

Patton, James M., Jr, Stough, H. Paul III, and DiCarlo, Daniel J. "Spin Flight Research Summary." SAE Paper 790565. Wichita, KS: April 1979.

Silver, Brent W. "Statistical Analysis of General Aviation Stall Spin Accidents." SAE Technical Paper No. 760480, April 1976.

Stowell, Rich. Emergency Maneuver Training. Ventura, CA: Rich Stowell Consulting, 1996.

Stowell, Rich. From NACA to PARE®: Unifying Spin Recovery Information Disseminated Over the Last 57 Years. Ventura, CA: Rich Stowell Consulting, 1993.

Stowell, Rich. "How Safe Is Stall/Spin Awareness Training?" Sport Aerobatics, June 1998.

Thompson, William D. Cessna--Wings for the World. Bend, OR: Maverick Publications, Inc., July 1992.

Veillette, Patrick R. "Re-Examination of Stall/Spin Prevention Training." Transportation Research Record, No. 1379, National Research Council, Transportation Research Board, 1993.

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