Carriers could face GPS software glitch next month

By John Croft

A software bug resident in a wide range of multi-mode GPS receivers (MMR) built by Rockwell Collins could cause datalink and other problems during the chronological transition from 20 to 21 June, cautions the European Aviation Safety Agency.

In a safety information bulletin (SIB) published 20 May, the regulator "strongly" recommended that operators with the units, which fly on practically all Boeing and Airbus models as well the Bombardier CRJ series, develop mitigation plans to deal with the potential problems, which were brought to EASA's attention by Rockwell Collins.

EASA says the error "may cause the MMR to compute a date that is 512 weeks or approximately 19.5 years in the past" unless the unit is powered on during the transition between the days (at 0000h GMT) or if an onboard source such as a flight management system or flight deck clock is set up to provide time to the MMR instead.

While the anomaly will not affect "position, integrity and time of day provided by the MMR," says EASA, it could prohibit the use of air traffic control datalink functions, result in incorrect date information on flight deck clocks, and possibly cause loss of maintenance and condition monitoring system data, as well as other anomalies.

Rockwell Collins says through the course of GPS system development and product regressiont tesing "our engineers discovered a minor software anomaly that affects the way the GPS receiver handles the date after June 20, 2009".

Stressing the anomaly does not in any way compromise navigation precision or integrity, the company adds: "We have been working closely with our customers and regulatory agencies to rapidly resolve this issue with minimal impact to our customers."