Originally Posted by
ElNull
My question here was not how an IRS do alignment. My question was that why not an IRS just take all the position from the GPS rather than taking time sensing and calculating.
As an aside, and this may come as a shock to the GPS fans, there are actually certain airports around the world these days where you will see evidence of GPS jamming on the ramp......In which case you revert (carefully) to the more traditional methods of telling the Inertial it's starting position - the sort of methods that I'm sure gums and others of a certain vintage are familiar with.
It's nice to have GPS available as a source for the present position at the start of the align process, if for no other reason than to reduce the risk of finger trouble during data entry leading to embarrassment, but there are reasons why it's not essential.