Originally Posted by
NSEU
Agreed, but with IRSs off, the IRS LEFT Advisory Message is removed (so the QRH statement is partially true). I even asked Boeing why BGS was still available with the IRUs off. They said it's just the way the logic works.
This makes sense. Perhaps when they were designing the system and came up with the requirements for Body Gear Steering activation(which is listed in an earlier post), the person with input from the maintenance point of view said that there would likely be situations where a maintenance crew wants to taxi the aircraft(in which case BGS would be desirable) yet all three IRU's will be selected off. Therefore Boeing designed the system to accomodate this situation after considering that there would likely never be a situation where pilots would be doing higher speed ground operations with three IRU's selected off, so it was therefore a reasonable design.
That would explain why the logic is the way it is. Covers the piloting side of things at for high speed ops as well as the maintenance side of things at low speed ops when it comes to BGS.