The AirSafe Journal - Issue 8

The AirSafe Journal
Issue 8 29 March 1997
Todd Curtis, PhD


The last AirSafe digest discussed issues of data analysis in light of the FAA initiatives to make more safety data available to the public. In what could be a example of things to come from the FAA, the NTSB released their 1996 U.S. accident statistics to the general public on 21 February. In spite of the large amount of data, there were still significant omissions and shortcomings in the NTSB information which reduced the usefulness of the data.

Also on 21 February there was a very interesting interview with the current Boeing vice president for safety and the former chairman of the NTSB about recent NTSB questions about the safety of the 737 rudder system. The NTSB has suspected, but not proven, that this system was involved in two fatal 737 accidents.

On 25 March 1997, the FAA announced that 33 carriers operating scheduled service with aircraft with a capacity of between 10 and 30 passengers had changed their operating procedures to use the same procedures as airlines flying larger aircraft. While the FAA proclaimed that this put the smaller aircraft on the same level of safety of larger aircraft, a close review of the press released reveals that this may not be the case.


Overview of the 1996 Accident Record

The NTSB press release served several purposes, it categorized significant airline and other aviation accidents in the U.S. since 1982, provided information on accident rates and fatalities, and defined some of the terms the NTSB uses to describe accidents. This is an important document for those who wish to understand the risks of U.S. civil air travel. It is however, a document with some flaws. There are some specific ways that my site and the NTSB present risk data, differences so significant that I am unable to use the NTSB data in this web site without further refinement and scrutiny.

The key question I had for the NTSB data was whether it was useful for the kind of risk statistics that I use in the Air Safety Home Page site. Simply put, the NTSB summary data in its present form is very difficult for me to use because it tends to combine several types of operations in their summary statistics. For example, the press release gives the accident rate per 100,000 departures for U.S. Carriers operating under Part 121 operations from 1982 to 1996. The problem I have is that Part 121 operations includes all flights by aircraft with a passenger capacity of at least 31 seats whether that aircraft was used in cargo or passenger service or if the aircraft were prop or jet driven. My key statistics deal with fatal passenger event rates. I would not be able to determine these rates using this table without extensive additional research. Furthermore, I tend to distinguish jet fatal event rates from prop aircraft rates. That is also not possible with the NTSB in its current form.

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737 Rudder System Interview

On 21 February 1997, the U.S. television news show NewsHour had an interview with the former chair of the NTSB and the current Boeing Vice President for airplane safety and performance. The interview focused on issues raised by NTSB concerns about the resolution of suspected rudder control problems with the 737. Specifically, the NTSB concluded that the current rudder system on the 737 does not provide the same level of safety as rudder systems on other kinds of passenger planes and that a malfunction of a rudder could no longer be considered an extremely improbable event.

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The Commuter Rule - Almost One Level of Safety

In a 21 March 1997 press release, The FAA announced that 33 air carriers had successfully transitioned from operating their scheduled flights under Part 135 rules to operating under Part 121 rules. This effort was part of an initiative started in late 1995 to bring all airliner operating aircraft with a passenger capacity of between 10 and 30 seats under the same operating rules as airlines with larger aircraft. While there have been substantial changes in the operations of the smaller airliners, there are still some significant differences between the operations of these smaller aircraft, differences which have a direct effect on the level of risk faced by those who use the smaller aircraft.

The Commuter Rule grew out of a desire on the part of the Clinton Administration to eliminate the differences in accident rates between smaller and larger aircraft. In spite of the changes that have taken place, several significant differences remain:

  • Aircraft Design: While the Commuter Rule led to changes in airline operations, airlines will continue to use aircraft that are certified under standards that are not as high as the certification standards of larger aircraft. In fact, airplanes currently in production and the existing fleet will not have to meet many of these upgraded performance requirements and equipment installations.

  • Age 60 Rule: Currently, pilots of Part 121 air carriers have a mandatory retirement age of 60. Under the Commuter Rule, airlines have four years to implement this rule for pilots of smaller aircraft with a capacity of between 10 and 30 seats

  • Flight Crew Duty Times: There is a proposed rule change that would bring the flight duty times and crew rest requirements of the operations of aircraft with between 10 and 30 seats under the same rules as operations of larger aircraft. While the proposed rule is under evaluation, crew members of commuter aircraft will continue to be regulated under the flight and duty rest provisions in Part 135.

It is unclear what effect these differences in rules and requirements will have on the risks of flying on smaller aircraft with a capacity of between 10 and 30 seats. Whatever the effect, it would appear that the FAA claim that all airliners with a capacity of at least 10 seats are operating under the same safety rules and enforcement is not completely true.

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The AirSafe Journal - Issue 8 -- Revised: 24 May 2015