Litton Aero Products is flight testing its LTR-97 fibre optic gyro-based system on a Boeing 727-200 as a strap-down replacement for potentially thousands of aircraft equipped with older electro-mechanical, vertical and directional gyros.
The market, estimated to be for around 5,000 systems, includes McDonnell Douglas DC-8s, DC-9s and MD-80s, as well as Boeing 727s, 737-200s and 747 Classics. The single box LTR-97 replaces two individual boxes in these aircraft, namely the Sperry-built VG 311 vertical gyro (VG) and the C-9 to C-11 directional gyro (DG). Weight of the single unit is also half that of the current configuration, says Litton.
"We are looking at something like 10 times the mean time between failure [MTBF] rate of mechanical VG/DGs," says Litton programme manager, William Hackman. "We are guaranteeing an MTBF of 12,000h to airlines, and the specification is actually much higher than that," says Hackman who adds that the older units are now affecting operations because of increasing failure rates and low dispatch reliability.
Litton says the LTR-97 is "the smallest, lightest, least expensive FOG-based unit on the market", and has been designed to interface with existing wiring to make the change-out easy. "We figure about 30min per aircraft is all it takes," says Hackman.
The current flight test plan calls for final evaluations on the 727 by the end of the year with a TSO (technical standard order) anticipated "maybe by the end of January". A supplemental type certificate (STC) on the 727 would follow by the end of February 1999, Hackman says.
Litton originally planned to have the STC/TSO by early October 1998, but admits that verification of some elements of the system have taken longer than expected. These include the intermix configuration, in which a single LTR-97 can replace one set (two original units), leaving a set of conventional VG/DGs in place. Litton engineers have also had to tackle interface problems with the aircraft's weather radar.
Operators tipped to adopt the change include FedEx, which has been working with Litton "a lot", says Litton. Others said to be interested include American and Continental Airlines. Initial production units will be shipped in March says the manufacturer.
Source: Flight International
