Auto-Coupled WAAS/DGPS Curved Approaches

[Badmachine]

Any reference material available regarding auto-coupled WAAS/DGPS curved approaches or auto-flight trajectories?

Thanx.

[Zeffy]

Better to think of WAAS and DGPS as nav sensors rather than approach procedures.

FAA's LPV minima for RNAV (GPS) approaches require WAAS. However, LPV procedures have no curved paths.

You may be thinking of RNP SAAAR (ICAO = AR) procedures with RF (Radius to Fix) leg types.

Examples:

Queenstown

Chicago Midway

Rifle, CO

FAA AC 90-101 has more information

[Badmachine]

Very helpful. Thanx.

Can auto-coupled approach procedures involving Radius-to-Fix turns be performed with non-GPS nav-aids or some combination?

[waren9]

Dont think so. That is the whole point after all, to get away from the disadvantages of ground based aids.

The approaches I'm familiar with are designed without reference ground based aids.

[c100driver]

Yes but why?

It is possible with DME/DME/IRS and an FMC that can use radius to fix (RF) legs, by using the DME/DME as an update for the FMC position.

[Badmachine]

Interesting.

In the case of DME and IRS, will the FMC generate some usable combined output during an RF leg?

[waren9]

In my experience, crews are not permitted to "build" approaches, they must be in the database from an approved supplier, and arent to be modified.

Sure, you can build an approach using whatever waypoints you like but during a GPS or RNP approach you are asking the aircraft to fly a track determined in space by GPS.

In fact, some approaches ask you to deselect nearby navaids to prevent the chance of any radio updating so you dont inadvertantly get EPE exceeding the limit for the approach.

[c100driver]

In the case of DME and IRS, will the FMC generate some usable combined output during an RF leg?

Yes the IRS provides the, (for want of a better term) raw data position information to the FMC and the DME/DME update refines that position in the FMC, the same as a GPS position would update the FMC position but with GPS it would to a better accuracy (lower ANP).

It is the FMC that "projects or draws" the RF leg for the aircraft to fly. All the DME/DME or GPS does to the FMC position is increase accuracy and thefore the confidence of the FMC solution being where it was designed to be (RNP) this confidence is expressed as ANP (in nautical miles) on the Boeings. If you lose DME/DME or GPS updating the ANP (confidence of the FMC solution) will grow at the IRS drift rate until ANP is greater than the RNP. The IRS/FMC position may actually be bang on, but the confidence of the position gets worse over time.

[Zeffy]

Can auto-coupled approach procedures involving Radius-to-Fix turns be performed with non-GPS nav-aids or some combination?

In the case of DME and IRS, will the FMC generate some usable combined output during an RF leg?

The ability of an FMS to fly various ARINC leg-types -- e.g., TF, RF, VA, CF, etc. -- is entirely separate from the position computation function.

Either the FMS can fly an RF leg or it cannot.

The sensors used to compute aircraft position are not relevant.


Having said that, I'm not aware of an FMS that is RF-capable that does not also have GPS sensors in the navigation array.

[c100driver]

Having said that, I'm not aware of an FMS that is RF-capable that does not also have GPS sensors in the navigation array.

Our B733 with update 10.7 are all capable of RF legs, even the ones without GPS installed. However only our B733 with GPS updating are approved for RNP AR operations.

It is the GPS sensor equipment that provides a small enough ANP to fly an AR procedure with RF legs.

[Badmachine]

Thanx for the info.

Is autopilot relied upon for legs with the lowest RNP values?

For an RNP leg of .1 for example, what ANP values are generally acheived by big Boeing and Airbus planes?