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Mango
7th May 2008, 01:26
I was wondering if anybody can tell me what the FCOM ref. is for the following issue that has been keepind me awake at night.

If GPS is deselected or not working what is the time limitation for IRS only navigation since last radio update?

6hrs springs to mind but I cant find the FCOM ref. to back this up.

Thanks in advance.

Mango

Down Three Greens
7th May 2008, 01:28
For what level of RNP? RNP-10 (i.e. Oceanic) is 5.7 hours.

FCOM 2.04.46

neilb767
7th May 2008, 01:41
Ya kind of wondered that myself.

strange that the B767 was also 5.7 hrs.. and that is no spring chicken.

Makes me wonder if the 5.7 hrs is a regulatory thing or if High Tech A330 designers used the old tech, boxed up, off the storage shelf 1970 technology IRS's.

.............. just answered my own question...it is a regualtory thing.

Fcom 2.04.46 P3 says..

As per FAA notice 8400 this limit is

6.2 hrs from irs gnd alignment or 5.7 since last fm update...


Im new on the bus, so how do you know when the last update was?

On the boeing , you got an IRS NAV only message, ( which meant that the last update was 12 mins ago) is it the same on the Bus ???

The buses Im flying all got space nav, have only had one flight with no GPS avail.

Iceman49
7th May 2008, 04:21
Ours reads: Unlimited with GPS as part of a Multisensor system. 18 hours with ADIRU only beginning when the ADIRU is selected from ALIGN to NAV. 17.7 hours with DME/DME updating beginning each time a DME update is received. (RNP Type: RNP - 10)

Mango
7th May 2008, 08:24
Sorry, it was for RNP-10.

Thanks alot, "Down Three Greens" and "neilb767" FCOM 2.04.46 is what I have been looking for.

Iceman49, I dont understand the 18hr and 17.7hr bit with regards to flight time outside radio navaid coverage for aircraft without GPS (RNP-10)?

Cheers,

Mango

Iceman49
7th May 2008, 16:48
Our aircraft can takeoff, lose all GPS and continue on an RNP10 segment so long as it does not exceed 18 hours (no air to air), if fact we can dispatch without any GPS on an RNP10 segment again as long as the segment does not exceed 18 hours. The 17.7 comes from fmc updates vs the 18hrs from IRS only.

Down Three Greens
8th May 2008, 02:06
Iceman. Some ADIRU's have extended time limits and I guess this would apply to your aircraft. This was brought about to allow non-GPS aircraft to cross the Pacific without GPS and maintain RNP-10 capability. It normally involves a proof of ADIRU performance study. The standard A330 (and A320 for that fact) is as detailed above.

DTG

Iceman49
8th May 2008, 04:41
On our original ops spec we had the 6.2 and 5.7 limitation...after a trip to Airbus, we got the extended limits with concurence with the Feds. We have been operating the 330 since 03 and have had only 2 problems with the loss of GPS and I think it was traced to the MMR. Still much better than having the navs make wild excursions prior to the ADIZ, our 320s operater under the shorter time limits;)

Back Seat Driver
9th May 2008, 11:05
A318/319/320/321s, A330s and A340s without GPS PRIMARY
The navigation system of these aircraft consists of 2 FM, 3 IRS and radio navaid sensors. The FM uses radio sensors for position updates or the mixed IRS position, if radio position is lost. This navigation system is certified, in compliance with the AC 20- 130A, as indicated in the Flight Manual. This navigation system also complies with the JAATGL2 (ACJ20 X4, AMJ 20-X2) for European Basic RNAV and TGL 10 for Precision RNAV in terminal area.
For these aircraft, navigation performance is mainly determined by the radio navaid ground infrastructure. In the European airspace, the operators can assume that the navaid ground infrastructure will support the RNP for Basic or Precision RNAV.
Outside radio navaid coverage (when in IRS ONLY), the RNP-X Type of capability will be maintained during a certain lapse of time, based on the demonstrated IRS drift rate, starting at the last IRS ground alignment or FMS radio update.
This navigation system is considered to meet all RNP-10 requirements during 6.2 flight hours since the IRS is placed in navigation mode, or 5.7 flight hours when the FMS discontinues radio updating. If the FMS is updated enroute, the Operator must demonstrate the effect of update accuracy on the time limit or may use the half-hour time reduction for automatic VORDME updates indicated in FAA Order 8400.12A, 12,e.
Authorities in charge of a particular airspace may specify a different time limitation (refer to ICAO Doc 7030).
In reference to FAA Order 8400.12A, aircraft eligibility for RNP-10 is classified in Group 2, paragraph 12.b.(1);(aircraft with FMS and ND).