RNP Certification For Mil GPS

[Kaiza]

G'day,
I was just wondering whether anyone here has been involved with, or knows anything about achieving RNP certification using EGIs that use P/Y code?

Does anyone operate an aircraft with EGIs like this? If you use an additional, seperate civilian GPS to get around the certification problems, do you then deselect the EGI so it does not provide part of your blended solution in RNP airspace?

Cheers

[threeputt]

This should be good!

3P:ok:

[Been There...]

Oh yes, what fun we had at the A400M meetings discussing this!!

As far as we could work out, the crews were supposed to select civil flight mode on the FMS which would use civil GPS for the positional solution and then military mode on the FMS for military (non-EASA/FAA/CAA) operations.

When we said to Airbus that the crews would just fly around with Mil GPS selected they weren't very happy :)

Come up against something Kaiza?

[Mactlsm1]

Try this link, doesn't look to difficult to me.

http://www.honeywell.com/sites/servlet/com.merx.npoint.servlets.DocumentServlet?docid=DD2A4EB58-6B7E-EEFD-A52E-8CA0D6E38FCA

Mac

[Lurking123]

That makes sense. Use the less accurate, less protected signal for an instrument approach.:confused:

[Kaiza]

Thanks "Been there", I thought concept of operation and actual operation might have some large differences.

I am on an aircraft project at the moment, the aircraft has not recieved any RNP certification yet, it is still a work in progress. We have dual EGIs and dual FMS's with embedded GPS. From what I can tell the FMS GPSs will be the only RNP certified long range nav source. The idea is- FMS for route nav, EGIs for tactical. The problem is the FMS blends its solution from the EGIs. I am just trying to figure out what the implications of this are.

EDIT: I know what you mean Lurking- accurate enough for precision weapons but not enough for an instrument approach....

[ARINC661]

I am working on a project with similar issues. To legally fly RNP requires a GPS with RAIM and has been TSO'd. Although we have a Honeywell EGI with RAIM it is not TSO'd and thus not acceptable to civil authorities.

The solution, as mentioned above, is to add a civil certified GPS and allow the crews to select the civil GPS solution, which is independent of EGI data. Whether they will is up to them, however they can claim that they have an RNP capable navigation fit. An alternate GPS was required by the safety case so the civil GPS solves two problems.

[WeekendFlyer]

I know a bit about this; PM me if you want more info.

The bottom line is that all RNP requirements such as BRNAV and PRNAV specify 3 things: nav accuracy, FMS functionality and system integrity. Where most military transport aircraft fail is on the integrity side, because they typically have only one EGI (or separate INS and GPS), and their GPS receivers usually don't have RAIM. What people sometimes confuse is that although P/Y code GPS receivers are more accurate and jam-resistant, without RAIM they are just as suceptible as C/A code GPS receivers if data from one of the satellites being tracked is erroneous.

The relevant regulations require civil aircraft to have RAIM GPS (see JAA TGL3& TSO C129a) or a "RAIM equivalent" system (such as INS auto-updated with DME - but this is no good for oceanic ops).

So if you want a military transport aircraft to operate in civil airspace, basically you will need to ensure it has a certified RAIM GPS. The other thing is to make sure that with the RAIM GPS selected, the FMS is not using a blended nav solution which includes data from a non-RAIM GPS source (such as a military EGI). The whole point of RAIM is that it is there for the day when one of the GPS satellites goes wibble and broadcasts incorrect signals, leading to GPS position errors. A non-RAIM GPS would be none the wiser and thus calculate an incorrect position, whereas a RAIM GPS receiver would detect the faulty satellite and, if it had FDE, isolate it and remove the erroneous signals from the nav solution.

Have a look at the ECACnav website PRNAV pages for more info. JAA TGL 10 is also a useful read.

[ion_berkley]

No kidding? P/Y code receivers don't typically have RAIM? What's the reasoning behind that? (assuming you can discuss that here). I've only worked on the design of C/A receivers but I assumed at this point that RAIM was ubiquitous in all modern designs....then again modern and military are two words that don't belong in the same sentence due to the length of the typical design cycles.

[Kaiza]

Thanks for the info Weekend Flyer. The EGIs we have do have RAIM but are not certified. The FMS solution we will be getting will be a blend of certified civilian GPS and intertial only information from the EGI. Because the EGI is non-certified does that mean it is effectively "corrupting" the solution, or does it not matter as we are only using the intertial rather than the GPS?

[WeekendFlyer]

Ion,

seriously - a lot of P/Y code GPS receivers don't have RAIM. There are a few out there but they are relatively new. A lot of military transport aircraft were upgraded to use GPS in the late 90's (e.g. USAF Pacer Crag programme for KC-135s), before RAIM was mandated for civil transport aircraft. Also in a lot of countries there was an exemption from RNAV equipment requirements for government/state operated aircraft, which was fine in theory but these days airspace is so crowded most ATC units are likely to refuse a non-RNAV flightplan in RNAV airspace, or else give a very sub-optimal route with delays.

Kaiza,

if you can be absolutely certain that the EGI is providing only inertial data and NOT blended inertial/gps data, then you should be ok. I know some EGIs transmit the raw INS, raw GPS and blended solutions on the databus, but not all. I would be extremely surprised if a FMS nav solution consisting of civil RAIM GPS blended with inertial data was not acceptable to the certifying authorities, because the RAIM GPS will always drive the long-term accuracy of the solution.

Out of interest, will the crew have the ability to select the EGI GPS as an alternative? If so, there will probably be a requirement to warn the crew when this is selected as the nav source, as the aircraft would then not strictly be capable of maintaining the RNP under civil regulations.

[Brain Potter]

Military aircraft have no obligation to meet any civil airworthiness criteria.

The Military Airworthiness Authorities may choose use the civilian regulations as a source of "best practice" when authorising a certain type of aircraft to perform a particular role or to operate in a particular types of airspace.

The concept of military "exemptions" is rooted in the response of the military airworthiness authorities after an aircraft type has been identified as failing to meet (a change to) parallel civil standards. For example, in the case of equipment required for access to certain airspace, the military authority may decide that their aircraft is equipped to their satisfaction and may allow it continue to operate in such areas - this is perceived as a military "exemption". Alternatively, the authority may decide that they are not willing to accept the risk of allowing such an aircraft to operate in that airspace with equipment that doesn't meet civil standards and it's Release-to-Service will be amended accordingly. In my experience, the military authority usually accepts the civilian regulation. This maybe partly because they cannot afford the staffing to build a case for taking their own view or simply because they do not have the appetite to shoulder any more risk than necessary. However, I would expect that the US Military Airworthiness Authorities are a little more bullish about their own primacy than is the case with smaller and poorer countries.

The cause of military "exemptions" being seen as forcibly revoked is usually down to the clashing requirements of different nation states. The British Military Airworthiness Authority may decide that it's transport aircraft do not require an ACAS system, but if the German authorities see it as necessary, then they can prevent access to their national airspace by denying diplomatic clearance.

Kaiza, If your nation's military airworthiness authority decides that the aircraft has sufficient navigational performance then they can declare it RNAV compliant, regardless of the civil certification status of certain elements of it's navigation suite.

[Kaiza]

WeekendFlyer, thanks for the info- yes the primary solution seems to be a blend of FMS GPS and pure inertial, so hopefully we should be OK. If the FMS GPS fails then it will go to the EGI hybrid solution, so in that case we would not be RNP compliant as you have said.

Brain Potter- thanks for the info, unfortunately, despite knowledge of this one of the project spec requirements was for the aircraft to be RNP compliant, so we dont have too much choice.

Thanks for the input everyone.

Cheers

[Jumping_Jack]

Blimey.....:bored:

[Blacksheep]

Military aircraft have no obligation to meet any civil airworthiness criteria.Perhaps, but RNP isn't simply a matter of airworthiness. (Nor for that matter is RVSM.)

RNP is an operational requirement, applied to aircraft that wish to fly on published airway routes under civil ATC, that happens to include airworthiness considerations along with the specific operational procedures. While "state" aircraft enjoy certain exemptions, when they wish to share a specified airway with civil traffic, they must meet the published criteria or fly "off-airway". In the crowded skies over Europe, that isn't really a practical proposition.

[Sir George Cayley]

Check out the TSO C145a/146 spec. The will account for SBAS. In Europe this = EGNOS

Also, integrity monitoring can include error detection so individual TSO C129a could comply.

In any case, within European CAS for the foreseeable future ANSPs will still be able to approve non compliant "legacy" a/c like the A400M:sad:eek:

Sir George Cayley (enroute the Civil side)