Serious tailstrike incidents prompt demands for software to detect data input errors
Honeywell will have to modify its flight management system (FMS) software to provide warnings to crews when unsafe or inconsistent performance or weight data is entered, if a new US National Transportation Safety Board (NTSB) recommendation is mandated by the Federal Aviation Administration. US airlines would also be compelled to incorporate the modification, prompted by serious tailstrike accidents which occurred in two different aircraft types because incorrect data was entered into the FMS.
The two tailstrike accidents came despite Boeing issuing warnings on the types of transcription error that can result in incorrect aircraft weight, fuel or payload data being entered, and incorrect speeds being displayed as a result. Another possibility is crew setting speeds independently that are inconsistent with the FMS calculations.
Quoted examples included a March 2003 Singapore Airlines Boeing 747-400 at Auckland, New Zealand, that was rotated at a speed 33kt (60km/h) below the 163kt required for take-off at the aircraft's actual gross weight, causing a massive gash in the lower aft fuselage; and a November 1998 Delta Air Lines Boeing MD-11 tailscrape landing at Portland, Oregon. The aircraft approached at lower than its reference speed because the FMS had accepted entries that made its landing weight less than its zero fuel weight for the trip.
The NTSB recommendations are that Honeywell should modify its FMS software – and user airlines must adopt the modification – to achieve the following aims:
* warn crews "when a take-off reference speed is changed by a value that would impede the aircraft's ability to safely take off";
* prevent entry of aircraft weights that would result in landing weights below zero fuel weight or operating empty weight;
* inhibit manual entries in the gross weight field or allow the take-off gross weight to be uplinked directly into the FMS;
Honeywell has also been asked to check its FMS computers to identify any more changes that might improve error checking.
DAVID LEARMOUNT/LONDON
Source: Flight International
