Thanks Avioniker.
Apart from having actually done an overspeed test, I seem to have all the data you have. The DEU's, of course, have all that IRU data for a thousand and one purposes, but our books don't always tell us what each bit of data is used for.
I would have leaned the other way towards purely airspeed, otherwise the trend vector would no longer represent airspeed, but an increase in aircraft inertial acceleration. The aerobaticists amongst us can probably tell us the difference between the two and how it affects aircraft behaviour.
If the trend vector was purely inertial, what indications would you get on your MASI if an aircraft was accelerating along the runway and was suddenly hit from behind by a large gust of wind? Would the indicated airspeed rate of increase reduce or stop and the trend vector remain at the same magnitude? (or even increase due to the force of the wind).
Thanks.
Regards.
Q.