The significance of FAR Part 25 certification
Even the most ardent fan of Big Government regulation would have to admit that the Federal Aviation Regulations comprise an especially monumental body of law. Fortunately, there is some method to its often Byzantine madness. Because it is organized into smaller, more easily digestible parts, we can conveniently ignore whole sections that don't particularly pertain to our own corner of aviation. Quick case in point — what is contained in FAR parts 13 and 171? If neither "Investigative and Enforcement Procedures" nor "Agricultural Aircraft Operations" immediately sprang to mind, chances are you (a) never got in trouble with the Feds and (b) are not crop-dusting for a living.
Part 25 of the FARs is one of those regions into which most of us tend not to venture very often. It prescribes airworthiness standards for the issuance of type certificates for transport category airplanes. As such, it is heavily laced with some pretty arcane language — stuff that only an aeronautical engineer could love. Nevertheless, since many turbine aircraft are certified to these standards, it is enlightening to sample a few of its highlights.
Because transport category aircraft by their nature are likely to be used for the carriage of paying passengers, it follows that the Feds would raise the bar a notch when it comes to their airworthiness standards. By analogy, Part 25 is to aircraft certification what Part 121 (dealing with air carriers) is to operating rules and regulations — a generally more stringent and comprehensive body of regulations than those pertaining to not-for- hire operations. The light single- and twin-engine aircraft that most of us fly fall under the purview of Part 23, which describes airworthiness standards for normal, utility, aerobatic, and commuter category aircraft.
Some of the distinctions between parts 23 and 25 certification are slight, while others are considerably more important from a pilot's perspective. An example of the latter is found in FAR 25.111. It dictates that if the critical engine on a two- engine transport category aircraft becomes inoperative at a point at which the takeoff may be continued, the aircraft must be able to maintain a minimum climb gradient of 1.2 percent, from 400 feet above the takeoff surface until completion of the takeoff phase. (This is usually defined as when the aircraft reaches 1,500 feet above the takeoff surface.) By comparison, Part 23 makes no similar demands of normal, utility, or aerobatic category multiengine aircraft. Thus, following an engine failure at takeoff, the pilot of a Beech Baron, Piper Aztec, or similar light twin could be faced with a zero or negative climb gradient under certain weight and density altitude conditions. A Gulfstream III or Boeing 777 pilot, on the other hand, would always be assured of at least a minimum single- engine climb capability under any takeoff conditions for which those aircraft are certified.
Pilots of transport category aircraft should also be happy to know that their aircraft must satisfy a higher standard of in-flight damage tolerance. For instance, FAR 25.571 prescribes that an aircraft must be capable of successfully completing a flight after striking a four-pound bird at cruise speed between sea level and 8,000 feet. Likewise, in the event of an uncontained engine failure, or fan-blade impact, the aircraft must remain safely controllable to a landing. Separately, the empennage structure must be able to withstand an eight-pound bird strike, and the windshield a four- pound bird strike, should either occur at cruise speed. Aircraft certified under Part 23 are not specifically required to satisfy any of these in-flight damage conditions. (For anyone who may be wondering, both parts 23 and 25 completely ignore the ever- fascinating subject of an engine's appetite for ingesting birds. Instead, it is discussed in all its gory detail in Part 33, "Airworthiness Standards: Aircraft Engines." But for those horror fans out there who absolutely need to know, a jet engine must be capable of devouring up to eight 1.5-pound birds in rapid succession, under takeoff-power conditions, without suffering serious indigestion. That is, it must still develop at least 75 percent power. It must also be controllable to a shutdown after feasting on a single four-pound bird, without destroying the engine or causing other related aircraft damage.)
Flight control design is another area where Part 25 sets a more exacting tone than does Part 23. For example, FAR 23.395 generally requires that flight control systems be designed "...to provide a rugged system for service use, considering jamming, ground gusts, taxiing downwind, control inertia, and friction." Contrast this with FAR 25.671(c). To paraphrase, aircraft must demonstrate capability of continued safe flight following (1) any single failure of a mechanical or hydraulic flight control component; (2) any combination of failures not shown to be extremely improbable, such as dual electric or hydraulic system failures; and (3) any jammed flight control condition that might be encountered, unless such a jammed condition is extremely improbable or can be overcome.
FAR Part 25 also mandates certain additional equipment not required on normal, utility, and aerobatic category aircraft. For instance, all designated fire zones (generally referring to engines and auxiliary power units) on transport category aircraft must be equipped with fire detection and extinguishing systems. Such aircraft must also have a takeoff warning system that will automatically provide an aural warning to the pilot at the start of the takeoff roll if the wing flaps or leading edge devices are not in the normal takeoff positions, or if speed brakes or longitudinal trim devices are in a position that might preclude a safe takeoff.
Perhaps the single most distinguishing safety feature found on transports is an extra pilot (and, at times, a flight engineer as well). Although nowhere is it specifically written that more than one pilot is needed, the criteria for determining minimum crew — spelled out in Appendix D of Part 25 — almost invariably produce that result. (There are exceptions to everything. Some 500-series Cessna Citation aircraft certified for two-pilot operation under Part 25 may be flown single pilot, if that pilot completes special training and receives an FAA waiver.)
Does all this mean that transport aircraft are inherently safer than normal, utility, or aerobatic designs? Certainly, tougher airworthiness standards must count for something. An airborne emergency involving an engine fire, for example, is likely to have a better outcome in an airplane equipped with engine fire detection and protection systems than one without. Accident statistics show that transports consistently top the list for safest operations.
The real reason for the fine report card, though, probably relates more to how the airplane is operated than to the certification standards themselves. Since pilots of these airplanes are apt to be flying for a living, they typically attend regular recurrent ground school and simulator training sessions. As part of a crew, they operate under a set of highly standardized, well- practiced procedures. They fly frequently, so rusty skills are less of an issue than for pilots who fly only occasionally. Often, they conduct flight operations under more restrictive (and expensive) operating rules, such as those in Part 121, that mandate a long list of additional safety enhancements for both crew and aircraft. It's an easy bet that any airplane's safety record, regardless of its certification category, would improve if flown in this manner.
Different aircraft and operational standards exist for a reason, which boils down to this: Not all aircraft missions are created equal. The fact that the FAA imposes higher standards for flight operations involving paying passengers doesn't mean that other operations must somehow be inherently less safe. Flown comfortably within the limits of both pilot and aircraft, any flight can be conducted with a high degree of safety. Unfortunately, accident records are replete with tales of pilots who failed to understand this point.
Look at it another way. Only a minuscule percentage of airline transport aircraft accidents over the years have been blamed on either outright mechanical failures or lack of technical proficiency on the part of crews. But a solid majority of accidents had their roots in human failures of other kinds, such as miscommunications, loss of situational awareness, or failure to adhere to standard operating procedures. In other words, pilot judgment and ability will always be the great equalizer, regardless of how well an airplane is built.
