gps app-737

[alexban]

Hy
are you doing GPS approaches on the NG? Is it allowed?
I've read that the FMS is allowed by the FAA for GPS app if the RNP is .03
What about outside the US?
I was told that you should check RAIM ,in order to be able to do a gps app.Also ,on some other types you can check what satelites are in use,you can deselct some of them....
This is not possible on the NG,nor even on the 777 I was told.
Or this is necessary on planes that use GPS as a sole mean of navigation?
Brgds
Alex

[reynoldsno1]

If the aircraft is fitted with an IFR certificated GPS as part of its fit, then, yes, you can fly GPS approaches. RAIM, per se, is not required if the GPS is integrated with the FMS - the integrity function is part of the FMS.
I don't know why you would want to manually deselect satellites -GPS only uses the "best 4" for the navigation solution anyway - any others available are used as for RAIM.
There are RNP0.3 approaches available outside the US. AFAIK, nothing below that figure - yet. Some airlines are looking for NG special approvals down to RNP0.1

[Yusef Danet]

In at least one country 737NG can fly RNAV-GNSS v approaches with GPS updating to RNP of 0.15. RAIM is irrelevant, the FMS position algorithims are coplaex enough to work out its own Circular Error Probable and if insufficient accuracy from the FC position is received...ANP exceeds RNP, missed approach required.

[piontyendforward]

The NG B737 cannot fly GPS approaches, RNP/ANP or RNAV yes but not GPS. Some countries allow an LNAV/VNAV overlay approaches but usually only with VOR/LLZ/ADF approaches

Air Canada and Alaskian had GPS CDU units on their Legacy and Classic aircraft and could fly GPS Approaches

You are required to de select the GPS from updating when flying in non WGS84 countries due to map datum errors.

The GPS units fitted to most Glass Boeing B737 are automatic and have no pilot interface, they are unable to show RAIM forecasts as required by an approach cert GPS. Hence the aircraft do ANP/RNP approaches.

[alexban]

pion:
newsflash: "Boeing airplanes using FMS as the primary means of navigation guidance have been approved by the FAA to fly GPS approaches provided an RNP of 0.3 or smaller is used.A manual entry of 0.3 RNP is requird if not automatically provided."
FCT 737 OCT31,2004

The FMS uses multiple sensors for position updating to include GPS,DME-DME,VOR-DME,LOC-GPS and IRS.It is a FAA certified RNAV equipment that provides lateral and vertical guidance referrenced from an FMS position.
About the RAIM,YUSEF is perfectly right.It's not required in this case.
Never heard of a 'RNP/ANP' approach,but I guess you're refering to RNAV approach,right?
Brgds Alex

[piontyendforward]

Alex,

We may be arguing symantics but in this case symantics are important to the system fitted to the aircraft. The B737 NG cannot fly GPS approaches, only the FMC has access to the GPS unit, it is automatic and has no operator interface. It has no RAIM facility to check RAIM prior to flying a GPS approach (remember it is a requirement to have RAIM for a GPS approach, and please read to the end of the reply before hitting the keyboard). That is for a GPS only approach.

However the NG have a better system than RAIM for integrity and can fly LNAV/VNAV approaches that co-inside with a GPS approach, with GPS updating the FMC position and you are correct that the FAA has authorised approaches with a minimum of RNP 0.3 and with a few other riders if using the VNAV function. You are in essence flying an FMC approach, not a GPS approach.

Here is the difference, and it is important, with a non FMC aircraft on a GPS approach and a GPS failure occures a missed approach must be carried out i.e. you have had a navaid failure. With the NG and any other Boeing approved aircraft for LNAV approaches as long as the ANP is less than the RNP then the approach can continue. Symantic's maybe but it is a big difference.

RNAV, RNAV(GPS) and FMS are the interim generic term, as is RNP approaches. FAA, JAA, CAA etc are still discussing what to call these type of approaches and have still to come up with common charting and procedures etc, although GLS is the most likley at this stage. WAAS and LAAS are also to be intergrated as approaches. RNAV includes all sorts of equipment LORAN, VOR/DME (KNS88 types)

RNP approaches are still rare with only two RNP approaches Down Under so far but more on the way soon, and only Qantas 738's approved to fly them so far, with most in Alaska and Canada. Boeing are moving too only two type's of approaches very fast (ILS or GLS)

Things are changing very fast in approach technology and the 787 will push that even faster.

Fly safe and often
Regards P

[jetblues]

Hey pointy... interesting posts but not all correct sorry.

Virgin Blue have been flying RNAV/GNSS approaches in Australia for some time now using B737-700/800's.

They are brilliant, and most importantly very stable. They beat the hell out of an NDB approach into a smaller port when there are thunderstorms about.

More later.

[swh]

piontyendforward,

I thought the 737 does have RAIM, just not predictive RAIM. You can get predictive RAIM at dispatch time with Wx and Notams.

Thought the GPSSU provides GPS position integrity to the FMC by GPS RAIM. RAIM computes an actual containment radius/horizontal integrity limit that is a function of the actual detected error in the GPS position. For RNP 0.3 the FMC uses GPS RAIM, to see if it has the required RNP, if it doesn't you get a "UNABLE RNP" message.

Cannot do RNP 0.3 without GPS and 2xFMC, and at least 2xIRS.

I dont belive the GPS on the 737 meet sole means of navigation, but does meet primary means down to RNP 1.0 in most latitudes (higher latitudes generally have fewer satellites avaiable), and supplementary means for less than RNP 1.0.

Airbus have predictive RAIM +/- 15 minutes for the FMC destination and calculated arrival time with an option for another destination and arrival time. Its just a function of FMC software, nothing to with capability of either aircraft, in some cases its the same FMC manufacturer in both aircraft.

The 737 has better LNAV/VNAV display when flying RNP approaches, with the horizontal and vertical RNP scale shown on the PFD, the 737 has the G/S ghoast pointer, airbus has the doughnut, both have a vertical deviation scale on the PFD, the airbus doesnt have lateral deviation on the PFD, just the ND in FINAL APP.

Personally prefer the airbus GPS position monitor page over the B737 as it serves as a backup in the event of unreliable airspeed from the ADC and/or IRS, most probable never use it in my career in anger, just nice to have real time ground speed, track, and GPS altitude available from another source.

[Capt Fathom]

This is an extract from the Jan/Feb issue of Flight Safety Australia magazine, published by CASA.

If the Queenstown trial lives up to expectations,
Qantas intends to roll out RNP to Australian ports. The trial represents
the first time RNP has been used for approaches, landings and departures outside North America. Qantas is only the third airline in the world to use RNP procedures within the terminal area.

Whole Article Here

[reynoldsno1]

RNAV yes but not GPS

What do you think GPS is???

There are RNAV-RNP0.3 approaches at Auckland - and not just for trial.

Any RNAV approaches below RNP0.3 (like Queenstown) will be "specials" - i.e. specifically authorised for approved operators only