November 1997 Volume 40 / Number 11
Piper Comanche Safety Review
The Comanche and Twin Comanche were two of the most popular Pipers ever built. They were built in Lock Haven, Pennsylvania, from 1958 to 1972. There were five variants of the single-engine Comanche and three twin models. In the twelfth safety review that the AOPA Air Safety Foundation has done on specific aircraft, we looked at both the Comanche single-engine series and the twins and studied accidents that occurred from 1982 to 1992. Funds for this review were provided by members of the International Comanche Society who wanted to see how their favorite airplane stacked up against the Beech Bonanzas, Cessna Centurions, Piper Arrows and Lances, and the Bellanca Viking on the single-engine side. The twin challengers were the Beech Duchess and Travel Air, Grumman Cougar, and the Piper siblings: Apache, Aztec, Seneca, and Seminole.
In every aircraft that we've analyzed to date, pilots remain the primary causal factor in accidents, weighing in at roughly 75 percent. The comparison groups had similar numbers. During the 10-year period of the study, an average of 33 single Comanches and 10 Twin Comanches per year were involved in reportable accidents. In terms of accidents per 100 aircraft in the fleet, the single Comanche averaged 12, while the comparison singles had 9.6. The record of the Twin Comanche was virtually identical to that of the comparison twins, at about nine accidents per 100 aircraft.
Pilot background and experience is always a question. While we have access to flight hours and certificates, little is known about the training the pilot received initially or whether recurrent proficiency was anything more than a cursory biennial flight review (BFR). The graphs of total flight times for the Comanche singles are similar to those of the comparison aircraft. The lion's share of serious accidents involve pilots with fewer than 2,000 hours total time. That's not too surprising, though, since most of the pilot population either falls into that category or must pass the 2,000-hour mark to become a grizzled veteran.
If a pilot survives the first 100 to 200 hours in type, the chances of an accident go down dramatically. Sixty-four percent of serious accidents occur to single-engine Comanche aviators new to the breed. This is a trait common to every aircraft. It is so prevalent that the airlines require new captains to have higher instrument minimums until they attain 100 hours in type. Operating from longer runways and otherwise not flying the aircraft up to its performance limits early in the relationship would probably save GA pilots a lot of trouble.
For the Twin Comanche the hours and patterns are similar to those of other twins, with the exception of a well-defined spike for pilots having 1,200 to 1,400 hours total time. This is unique and accounts for fully one fifth of the serious Twin Comanche accidents. Before you rush to call the life insurance agent, however, understand that this represents only six accidents in a decade. We can't tell you why these pilots have such difficulty other than the traditional speculation of overconfidence and complacency.
There are some rather discouraging numbers concerning accidents occurring in instrument meteorological conditions. The Comanche singles racked up an astounding 17 accidents per 100,000 IMC hours, compared to less than half that number for the comparison group. ASF can discern no mechanical or aerodynamic reason why the Comanche should fare so poorly. The judgment — and, in some cases, the skill — of the pilots involved suggests that it is hard to be humble when you own a Comanche. In a capable cross-country airplane, a touch more humility frequently equates to survival. Night accident ratios yield similarly poor comparisons.
A few case studies will show some remarkable ignorance or stupidity. A 49-year-old VFR private pilot with 65 hours total time flew his single-engine Comanche 250 into an area of reported intense thunderstorms. Witnesses observed the aircraft descending minus a large section of wing.
A 1,200-hour private pilot attempted to climb his Comanche 260 with four passengers on board through a layer of severe icing. A sigmet warned the pilot of severe ice from the surface to 12,000 feet. The engine intake clogged with ice at 5,000 feet, and the alternate air apparently was not used or didn't work. The flight landed in a parking lot without injuries to anyone.
A 5,000-hour, 65-year-old CFI piloting a Comanche 250 made so many judgment errors on a night flight into the mountains that it's hard to know where to begin. The pilot departed without getting a weather briefing or filing an IFR flight plan. He attempted an approach that was below minimums and missed. He tried the approach again, realized that he was getting low on fuel, and decided to look for an alternate. The pilot finally realized that there was no alternate in range and found the ground on the third try. It just didn't happen to be the runway.
None of the above accidents had anything to do with the aircraft, but they definitely say something about some of the pilots who choose to fly the Comanche singles. Determining why certain people buy certain models of aircraft is not in my job description, so we'll have to be content with saying that some Comanche pilots just don't have very good judgment.
There are a few areas where the aircraft may inspire too much confidence. The fuel exhaustion rate is more than double that of the comparison aircraft. The Comanche is not a short-range aircraft, and there are numerous mods and tank configurations to extend an already generous fuel supply. At times, it seems that Piper never built any two alike, but one thing is certain — the pilot should supervise the filling of the tanks and ensure that the attendant is patient in letting the fuel disperse in the tank. Otherwise, there is a good probability that the engine will stop, perhaps 45 minutes earlier than expected. This trait is also shared with the Cessna Centurion series, but Comanche pilots should take little solace in that.
It's also extremely important to carefully and patiently check the fuel drained from the sumps during the preflight inspection. Comanches and Twin Comanches use a central drain arrangement that's activated by a knob in the cockpit. The idea was for the pilot to be able to drain all the sumps by using a single knob. While this may keep a Comanche pilot from crawling around under the wings on all fours to check each sump, the design lets gas drain on the ramp, and it can be difficult to see or collect fuel samples. Water or contaminants may not be noticed.
Inadvertent gear-up landings and retractions also seem to pose a problem for this venerable retractable. Mechanical problems aren't usually the cause — poor cockpit procedure or plain old forgetfulness catches the majority of pilots. At the recent International Comanche Society convention, one of the members pointed out that there had been 10 or so gear mishaps within the last month. One pilot even joined the gear-up club in his Twin Comanche at the convention. No one is immune to this and, again, humility and good procedure seem to be the best preventive measures.
The Twin Comanche used to have a terrible reputation as a flat spinner in the late 1960s and early '70s. This is more a reflection of how the aircraft was used than a design failure. FAA required low-altitude VMC demonstrations, and some pilots were practicing single-engine stalls. As a low-priced twin with economical operation, the PA-30 was sold in large numbers to flight schools. Instructors frequently failed engines shortly after takeoff to help students perfect their engine-out skills.
The aerodynamics are fairly obvious in retrospect — a yaw suddenly introduced by asymmetric thrust of a simulated failed engine during slow-speed flight, a slight mishandling by the student, and presto — stall, roll, spin. The low-speed corner of the aerodynamics envelope is not a safe place for multiengine pilots. The airlines discovered this in the 1960s when they lost far more aircraft in training than in actual emergencies, and so it was with the Twin Comanche.
By 1971 there had been 40 fatal Twin Comanche stall/spin accidents, and both the FAA and NASA had become involved. A fix was made, to both hardware and procedure. The FAA banned single-engine stalls on flight tests, banned VMC demonstrations at high density altitude where VMC and stalling speed would be close, and banned low-altitude stall demonstrations. An airworthiness directive was published raising the VMC from 80 mph to 90 mph, providing greater margin above the stall.
Piper furnished owners with a free airflow modification kit that included wing leading edge stall strips, a rudder seal strip, an aileron-rudder interconnect system, and rerigging of the rudder and stabilator. These changes were designed to provide better aerodynamic stall warning and controllability at slow speeds.
In May 1970, Piper also introduced a counterrotating right engine retrofit kit to eliminate some of the yaw introduced when the left engine fails. A new Twin Comanche — the PA-39, with counterrotating props as standard equipment — was brought into the Piper line. With the aerodynamic fixes and intelligent training procedures, the recent accident record shows the Twin Comanche to be a safe aircraft.
In most other areas the Twin Comanche matches or exceeds the fleet experience in safety. One minor exception, as with its single-engine sibling, is pilot-induced landing-gear mishaps. Out of 11 landing-gear accidents, six were attributed to inadvertent retraction during rollout; three were instances in which the pilot failed to check that the gear was down and locked; in one case the pilot did not use the emergency extension system; and in one training accident, the CFI didn't verify that the student had extended the gear.
As with any aging aircraft, maintenance is a priority. While we didn't note any particular problems with the Comanche, it is only logical that aircraft 25 to 40 years old will need significant attention. A few accidents highlight the importance. A Comanche 250's engine quit a mile from the airport. The pilot was unable to move the fuel selector, and the aircraft landed some 700 feet short of the runway. A service bulletin requiring a rebuild of the selector valve had been ignored. Shortly after takeoff, an oil line ruptured on a Comanche 400. The engine had been replaced, but the oil line was original equipment dating to 1964, 22 years prior to the accident.
The Air Safety Foundation salutes the International Comanche Society for its efforts to educate owners and assist them in maintaining these vintage high-performance aircraft. Their technical and financial participation in preparing this safety review shows a serious commitment. Anyone flying a Comanche or Twin Comanche would do well to become a member of this group.
The complete safety review is available from Sporty's Pilot Shop for $22.95 and includes model information, airworthiness directives, service difficulty reports, a complete training syllabus, and accident case studies. To order the review (product #M576A), call 800/543-8633 or fax 513/735-9200. For information on the International Comanche Society, contact the organization at 405/491-0321.
See also the index of "Safety Pilot" articles, organized by subject. Bruce Landsberg is executive director of the AOPA Air Safety Foundation.