Most, if not all, of the FAA’s requirements for carriage of flight recorders do not apply to piston-engined aircraft.
For instance, 14 CFR 91.609(c)(1) (emphasis added):
No person may operate a U.S. civil registered, multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration, excluding any pilot seats of 10 or more [sic] that has been manufactured after October 11, 1991, unless it is equipped with one or more approved flight recorders...
and 14 CFR 91.609(e):
...after October 11, 1991, no person may operate a U.S. civil registered multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of six passengers or more and for which two pilots are required by type certification or operating rule unless it is equipped with an approved cockpit voice recorder...
Even the NTSB’s repeated recommendations that the FAA require the general carriage of flight recorders still exclude piston-engined aircraft from this requirement; for instance, recommendations A-09-10 (emphasis added):
Require all existing turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135 to be retrofitted with a crash-resistant flight recorder system. [...]
Require the installation of a crash-resistant flight recorder system on all newly manufactured turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a flight data recorder and a cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135. [...]
Require all existing turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a flight data recorder or cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135 to be retrofitted with a crash-resistant flight recorder system. [...]
I can’t see any objective reason why an aircraft would magically have less need to carry flight recorders just because its engine happens to use thrusting pistons instead of a gas turbine - especially since turboprop aircraft are (mostly) required to carry flight recorders, and turboprop aircraft, other than having turbine-driven propellers, are little different from piston-engined aircraft (indeed, many turboprop aircraft are piston-engined aircraft whose piston engines have been replaced with turboprops).
If anything, it would seem that piston-engined aircraft would have a greater need for flight recorders, for a couple of reasons:
- Piston engines are orders of magnitude more prone to breaking down in midair than turbine engines are, making aircraft that use them more likely to crash (at least from engine failures), and, thus, more likely to generate an accident investigation, for which flight recorders are extremely valuable (this is, after all, their original and primary purpose).
- Large piston-engined aircraft are also generally considerably older than the vast majority of comparable jet and turboprop aircraft, for the simple reason that few if any manufacturers still produce large piston aircraft rather than jets or turboprops. Older aircraft, for a multitude of obvious reasons, are more vulnerable to crash-inducing malfunctions or failures than newer aircraft, and are also more likely to lack many of the safeguards built into newer aircraft; yet, a 70-year-old DC-3 that’s falling apart at the seams is not required to carry any sort of flight recorder, even in scheduled airline service, so long as it isn’t retrofitted with turboprop engines, while a brand-new Twin Otter doing exactly the same job is, for the sole reason that its propellers are turbine-driven.
- The vast majority of piston-engined aircraft are smaller general-aviation types, which are much more likely than large commercial aircraft to be piloted by people lacking a high degree of competence, or people in possession of a high degree of sloppiness, or habitual rule-breakers, or people with another reason they probably shouldn’t be flying; conversely, the vast majority of general-aviation aircraft are piston-engined, and, thus, even if every single U.S.-registered turbine aircraft were required to carry flight recorders, there would be little benefit for the general-aviation community. In contrast, nearly all long-haul passenger airliners, and most shorter-haul ones as well, are jet-powered, while the remainder (primarily feeder and commuter aircraft making short, low hops) overwhelmingly use turboprop engines; most large freighters are also jets (with some turboprops thrown in), while smaller freighters are primarily turboprops and smaller jets; and business jets (as the name indicates) use jet engines, while most corporate propeller aircraft use turboprops. Airline (both passenger and cargo) and corporate pilots are held to much stricter standards than a guy going sightseeing in his C-172, and, not coincidentally, crash far less often than general-aviation pilots do (and, even if airline and general-aviation pilots had exactly the same numbers of crashes per unit airtime, there would still be more general-aviation crashes than airliner crashes, for the simple reason that there are far more general-aviation aircraft, pilots to fly said aircraft, and flights made by said pilots in said aircraft, than is the case for airliners); thus, requiring turbine aircraft, but not piston aircraft, to carry flight recorders still leaves the vast majority of crashed flights flight-unrecorded.
Why do U.S. flight-recorder requirements, and recommendations and proposals for same, exempt piston-engined aircraft for no discernible reason?