Chelton expects software fix for FlightLogic EFIS this month

 - January 30, 2007, 10:53 AM

Chelton Flight Systems this month expects to issue a software revision to operators flying with the company’s FlightLogic synthetic-vision EFIS to fix a known anomaly that the FAA has said could provide misleading guidance under certain circumstances.

The software glitch can provide pilots with false guidance information when flying certain nonstandard departure and missed-approach procedures, according to the FAA. Chelton has issued a pair of Service Bulletins (150-045972 Rev. A and 150-045973 Rev. A) to fix the software discrepancies, which mainly affect instrument approach procedures with climb requirements of greater than 300 feet per nautical mile.

According to the Boise, Idaho avionics manufacturer, FlightLogic is designed to provide guidance for altitude legs with the length of the leg predicated on the climb performance of the aircraft. With the current software, the altitude leg is pre-computed on database altitudes and an assumed climb rate of 300 feet per nautical mile.

The software places a phantom fix (a waypoint symbol without a name) at the calculated end of the climb. This method does not take into account the aircraft’s actual climb performance, but is safe under most circumstances because 300 feet per nautical mile exceeds the standard TERPS climb rate of 200 feet per nautical mile. But in certain cases, such as departure procedures with required climb rates of greater than 300 feet per nautical mile, the current software will give “hazardously misleading guidance into non-protected areas on altitude legs,” according to the Service Bulletin.

A similar scenario arises on instrument approaches where the missed approach point in FlightLogic’s database is lower than the actual MDA or DH and the first leg of the missed approach is an altitude leg. Chelton provides a number of steps to detect if this is the case, but the manufacturer cautions that if workload does not permit the procedures outlined in the SB, then the missed approach procedure in the unit’s database should be considered erroneous. In all cases, the company added, the published approach plate takes precedence over the database approach guidance.

The second SB deals with the new Rnav (GPS) V Runway 8 approach to Juneau, Alaska, which includes incorrect government source coding that was furnished to Chelton and Jeppesen. In the FlightLogic database the missed-approach procedure shows a straight-out climb as the first leg of the missed-approach procedure, when in reality a tight left turn is required to avoid rising terrain to the east. A fix for this problem has already been issued, the company said.

Chelton expected to release a software update for the previously mentioned anomaly to FlightLogic users this month, which the company said would eliminate the flaws. In the meantime, pilots were being told to take extra precautions to make sure they comply with all published departure and missed-approach procedures.

Used by operators involved in the Alaska Capstone program, FlightLogic is the first EFIS certified with synthetic-vision and highway-in-the-sky guidance cues.