Industry: VLJ certification changes too strict

 - December 23, 2009, 5:59 AM

The comment period on the FAA’s proposed changes to Part 23 certification regulations governing very light jets (VLJs) has closed, and commenters on the proposal submitted approximately 30 opinions about the notice of proposed rulemaking (NPRM). Growth in the VLJ market segment was spurred by engine manufacturers’ development of small turbofan engines, and new regulations are needed to address issues that were not contemplated when Part 23 was originally written.

The new rules are aimed at easing the burden on FAA engineers during certification of jets under Part 23 regulations. The current workload involves too much processing of exemptions, establishment of special conditions and developing equivalent levels of safety findings. According to the FAA, the new rules would “standardize and simplify the certification of Part 23 turbojets; clarify areas of frequent non-standardization and misinterpretation, particularly for electronic equipment and system certification; and codify existing certification requirements in special conditions for new turbojets that incorporate new technologies.”

One of the key proposals is to change the one-engine inoperative (OEI) climb gradient for Part 23 jets. Current rules require a “measurably positive” OEI climb gradient for jets weighing 6,000 pounds or less (such as the Eclipse 500) and 2 percent for those with a maximum takeoff weight of more than 6,000 pounds (although the 2-percent requirement has been imposed only by special conditions). The new Part 23 rules would codify the 2-percent climb gradient for 6,000-pound-plus airplanes and add a 1.2-percent OEI climb gradient for jets weighing less than 6,000 pounds.

Other proposed changes affect stall speed references, flight characteristics, crashworthiness, engines embedded in fuselages, avionics, systems and placards.
Most of the comments were submitted by aircraft and engine manufacturers, both of which delved into extensive detail on the relative merits of the proposed new regulations.

Diamond Aircraft, which is planning to certify its single-engine turbofan-powered D-Jet this year, worried that the new regulations would impose on light jet manufacturers a burden that doesn’t apply to manufacturers of other aircraft types. “The NPRM suggests the turbojets should meet a higher level of safety than a reciprocating or turboprop aircraft yet the justification is not clear,” Diamond commented.

Cessna’s engineering department observed that the proposed rules may be too restrictive. “The NPRM identifies ‘turbojet airplanes’ as the targets for these new regulations. However, some turboprops exist that perform at higher speed, altitude and weight than some turbojet/turbofan airplanes, yet these turboprops would not be subject to the changed aspects of the proposed rule as written. Cessna Engineering proposes that the basis be strictly by a measure of performance.”