The NTSB has recommended that the FAA require the air data sensor heating system to activate automatically after engine start in new airplanes certified under Part 25. The recommendation comes in response to two similar events, one in 2002 and one in 2005, in which two Boeing 717-200s experienced gains and losses of altitude and erroneous airspeed indications in flight. The Board determined that the cause of the events was the pilots’ apparent failure to activate the air data heating systems and subsequent ice and/or snow blockage of the pitot tubes. The Board also recommended the modification of existing airplanes to incorporate the automatic activation of the system or cockpit warning systems associated with failure to manually activate the heating system.