Taking a closer look at the Part 135 record

 - December 7, 2007, 8:25 AM

Of 19 fatal accidents involving Part 135 jet operators from 1999 to the end of last year, 13 befell flights flown under FAR Part 91–that is, without paying passengers on board. That’s more than 68 percent. There have been only six fatal jet accidents involving paying passengers in the past six years–including air ambulance operators (but not including EMS helicopters). How does this play into the safety comparisons between pure Part 91 operators and Part 135 charter providers?

There’s been confusion involving the comparative safety records of Part 91 operators and Part 135 operators–largely comparing their relative safety records to those of the airlines. FAA statisticians have divined that non-scheduled air taxi under Part 135–as a whole–is far less safe than the airlines.

But narrow the discussion to jets only and there were just 19 fatal accidents involving Part 135 operators over the past six years. So-called pure Part 91 jet operators (classed as “corporate/executive”) accounted for five fatal accidents from 1999 through last year.

Part of the business aviation safety culture dictates that accidents always happen to “the other guy.” So when an accident does occur–particularly a high-profile fatal–it is human nature for pilots to point out all manner of differences between themselves and the accident crew. For the balance of this discussion, only fatal accidents involving professionally flown fixed-wing jet aircraft are considered. That excludes all helicopters, and piston and turboprop corporate and charter operators. It also excludes owner-flown aircraft of any description. This discussion is for the passenger considering the risk involved in boarding a professionally flown jet.

Interpreting the Accident Statistics
The numbers confused even the people at NBAA. In a press release, the association reiterated its stance that statistics show corporate aviation is as safe as the major airlines. The conclusion was correct–at least as far as jets are concerned–but the numbers used to arrive at the end result were confusing.

The association said that its statistician, aviation-safety expert Bob Breiling of Robert E. Breiling Associates, “defines corporate aircraft as turbine-powered fixed-wing aircraft flown by a professional crew. For these operations, the fatal accident rate is 0.014 per 100,000 hours–which is nearly identical to that of the scheduled air carriers (0.012 per 100,000 hours).” But those exact figures apply to only one year–2003. Review the 13 years shown in a chart on the same press release and the “corporate/executive” column shows a much higher aggregate rate of fatal accidents, as much as 10 times higher some years.

Breiling’s fine print on the chart, however, explains that the numbers on the press release reflect fatal accidents involving all corporate-flown aircraft (including helicopters, pistons, turboprops and so on). He has other figures that show that “corporate/executive” jets are comparable in safety to the airlines–but that blessing does not extend to turboprops; and the comparison involves all accidents, not just fatals.

Breiling’s definition of “corporate/executive” transportation is comprehensive. He defines the category as involving “aircraft owned or leased and operated by a corporation or business firm for the transportation of personnel or cargo in the furtherance of the corporation’s or firm’s business and which are flown by professional pilots receiving a direct salary or compensation for piloting.” That narrows the field to what one could call the traditional in-house corporate flight department.

Narrow the field further to exclude all but jets and there were only five fatal accidents over the past six years. Since all flights by such operators are flown under Part 91, determining definitively whether any of the accidents involved a positioning or training flight is much more difficult than with Part 135 operators.

Is It Part 135 or Part 91?
For the purpose of defining safety among Part 135 charter companies, Breiling considers any operator that flies its aircraft for charter–even if it does so only part-time–to be the same as a full-time dedicated charter-fleet operator. If such an aircraft is involved in an accident, Breiling considers it a Part 135 statistic, even if the flight was being operated under the auspices of Part 91.

Breiling contends that a crew trained and authorized to operate under the stricter regulations in Part 135 ought to be viewed the same, regardless of whether it actually conducted a particular flight under those rules. As one other observer noted, if a limo driver reported a perfect safety record with passengers in the back but had wrecked two cars on his own time, the customer would want to know.

But AIN asked Breiling to further refine his numbers to determine how many Part 135 operators’ fatal accidents occurred while the flight was operating under Part 91–that is, on positioning flights, training flights or other non-revenue operations. The reasoning was, if a charter customer wants to know what his chances are for a safe flight, he ought to be able to see the industry’s safety record with passengers on board as well as its overall record. The results were interesting and surprised even Breiling.

The fact that two-thirds of fatal accidents involving Part 135 operators occurred when the aircraft were flying under Part 91 further complicates the analysis. Does it mean charter operators are as safe as Breiling’s “corporate/executive” operators as long as there are paying passengers on board? Are charter crews really that much less safe when there are no passengers on board? And if so, why?

There may be some good reasons. One involves duty-time limitations. A charter pilot’s duty time includes revenue flight time, and the legality of adding Part
91 flights at the front end or back end of the duty day is one of the factors under consideration by the Part 135 aviation rulemaking committee (ARC).

Another reason is weather minimums–a factor in the November 22 Gulfstream accident at Houston Hobby Airport. The highly experienced crew left Dallas early to pick up former President Bush at Houston Hobby Airport, shot an ILS approach with weather reported below minimums and hit a pole more than three miles from the runway. Had the customer been on board, beginning the approach would not have been legal.

The current state of the charter industry–which relies heavily on privately owned, managed aircraft placed on charter certificates for part-time use–makes for murky waters when ascribing certain non-passenger-carrying flights to Part 91 or Part 135. Jacque Rosser, charter aircraft specialist for the National Air Transportation Association, asked, “For example, what if you are the owner of an aircraft based in Washington, D.C., and actively listed on a charter operator’s certificate? You happen to be in New York. The airplane is assigned a Part 135 charter flight from Washington to Boston, and you call the dispatcher and ask to have the aircraft pick you up to take you to Chicago. If there were an accident on the flight taking off from Boston–obviously flown under Part 91–would you say it occurred on a Part 135 positioning flight, or a Part 91 positioning flight?” Arriving at a better understanding of such conundrums is part of Rosser’s work on the Part 135 ARC.

The good news is that the numbers of accidents are so low that conclusions about one segment of the industry compared to another are statistically dubious. For trained statisticians such as Breiling, it makes much more sense to study each accident individually and draw conclusions about what mistakes were made rather than to infer that the broad culture of the industry segment was to blame– and that all other members are therefore guilty by association.

For instance, among the accidents the NTSB lists as conducted under Part 91, there are two experimental test flight accidents and a positioning flight involving a Part 121 carrier–obviously not even closely related to Breiling’s corporate/executive industry segment. Discount those and the statistics begin to sound quite different. Also, one of the Part 135 operators’ positioning-flight accidents involved a mechanical failure shortly after takeoff.

Finally, using the airlines’ safety numbers as a benchmark will likely always cast business aviation in a bad light. Scheduled airlines will always win the battle for better safety statistics as long as the per-100,000-hours format is used. Business aviation–Part 135, Part 91 or whatever–doesn’t come close to flying the number of hours airlines fly annually.

But look at it this way: statistics show you’d need to fly 10 hours every day in an airliner for 1,800 years to be killed in an accident. So even if charter flying is 2.5 times as dangerous, you can still tell your customers they’d  have to maintain the same 10-hour-per-day flying schedule for 720 years to be killed in a chartered business jet.