Citation Longitude / LCR-100N vs Laseref VI

[Curt Chambers]

On the new Longitude it appears it comes standard with dual Northrop Grumman LCR-100N "Hybrid Navigators" that are full AHRS units with fiber optic gyros & GPS input and inertial positioning with the loss of GPS. As an option you can swap those for Honeywell Laseref VI Inertial/GPS units with laser based gyros.

My question is why? I though the fiber optic gyro units were newer technology....are they not as accurate as the laser units? I just assume the Honeywell units are more $$ - are they that much better.

Not planning on buying a Longitude anytime soon (JUST shy of the $29 million I need ) but I'm an avionics geek.

Thanks for any insight!

 

[Captain Bubba]

Many if not most jets will have an IRS(s) that use multiple sources besides GPS including Lasertrack, and VOR/DME. The reason being worldwide positional accuracy is important and SBAS isn’t available everywhere. There’s a priority matrix that uses the most accurate source and falls back to others when the primary doesn’t work.

 

[Curt Chambers]

Many if not most jets will have an IRS(s) that use multiple sources besides GPS including Lasertrack, and VOR/DME. The reason being worldwide positional accuracy is important and SBAS isn’t available everywhere. There’s a priority matrix that uses the most accurate source and falls back to others when the primary doesn’t work.

Yep - totally get that. My question was more that the Northrop FOG based unit and the Honeywell RLG unit both seem to offer a very similar feature set: Hybrid Inertial/GPS when GPS data is available and a fallback to inertial positioning when GPS is degraded. I wondered why someone would elect to switch to the Honeywell units? I pretty much figured in the leg lengths we are talking about there wouldn't be much difference between FOG and RLG gyros - but maybe there is?

 

[Curt Chambers]

....and down the rabbit hole I went....Actually JUST got an answer back to my question from a contact at Textron. Longitude operators will option the Honeywell Laseref units IF they need the capability of "Required Navigation Performance AR (Authorization Required) Approaches" which require an "RNP value of less than .3"...and an entire BUNCH of technical requirements on maintaining that accuracy in the event of partial equipment failure. Just looked at one of those approaches and those are come terrain challenging approaches!