The FAA plans to clarify, but not change, its Part 25.1329h design considerations for manufacturers of aircraft low-speed alerting and protection devices.

To ascertain what clarification is required, the agency is seeking comments about its PS-ANM-25-16 policy, which evolved from a number of accidents and incidents in which flight crews were unaware that their airspeed was decaying. While the aircraft involved complied with standards in place at the time they were certified, the FAA now believes the operation of the low-speed alerting devices aboard some aircraft was simply inadequate.

The protections suggested in the new policy are designed to ensure that pilots are aware of low airspeed and can determine the appropriate actions, or that flight guidance systems do not fly the aircraft into a regime outside the normal flight envelope.

In one incident the crew of a 737 did not realize the aircraft’s autopilot and autothrottle systems had disengaged. The Boeing’s airspeed fell to 20 knots below reference speed, activating the stick shaker, before the crew recovered. In three other accidents–involving an ATR 72, a 737 and a Dash-8–the pilots also failed to monitor their airspeed. All three aircraft later stalled and crashed, with significant loss of life. Policy comments are due by March 10.