Originally Posted By: Astro14
Originally Posted By: fdcg27
You'd certainly know better than I.
In what areas or operational scenarios would INS be essential?
Are any current airliners delivered with it?
I had thought that these costly systems were mainly a thing of the past in an age of GPS.
As backups in mission critical applications like AF1, sure, but anywhere else?
GPS coverage, and accuracy, varies with the constellation visible. So, in mountain canyons, it can degrade to the point that it's unsuitable for use in aircraft navigation. One of our required checks before flying a GPS-based approach, is the RAIM (Receiver Autonomous Integrity Monitoring) prediction for accuracy. It has to be "good enough" to fly the approach.
So, a perfectly functioning GPS constellation, may not meet accuracy requirements for aircraft navigation.
That's why every new airliner built has a triple ring-laser gyros. ADIRU is the vernacular on an Airbus (each is integrated with an air-data unit). They provide both platform (attitude and heading reference) and dead-reckoning position to the flight management system...
The RockwellCollins NAV system (as do many others) updates the NAV database when GPS is visible.
When GPS is not available, the system defaults to INS and the INS provides updates from the last known GPS position, and then updates the navigational database from that point on until GPS comes back on line.