Cessna sent me a document, I will try to find it but it was in 2007. I simply cut and pasted the avionics spec when I did it again in 2011, as we found the avionics fit to be very good for our purposes.
Of course you might say Cessna would say that given that it added $80,000 to the aircraft, but I honestly don’t think they were that bothered, they would have preferred to make them all standard.
I have not found the Cessna documentation, but see
bottom of page 17
but that doesn’t say what I remember being the motivation to go to a dual FMS fit
That says
8.4.3 Intermixing of equipment
Simultaneous use of RNAV systems with different crew interfaces can be very confusing
and can lead to problems when they have conflicting methods of operation and
conflicting display formats. For approach operations, simultaneous use of RNAV
equipment which is not identical or compatible is not permitted.
which as you say doesn’t mandate a dual GPS installation.
However it is itself a useless rule – what does “compatible” mean? Typical useless European rulemaking – a load of people get together in a room, draft a reg, and eventually it becomes law without anybody competent in drafting having gone over it. So many EASA rules can be whatever somebody wants them to be, which is bad for aviation where there is a huge incentive (both financial and “emotional”) to gold plate.
Maybe you are talking about a business jet? What “Cessna” plane was this? I have never heard of such a requirement in light GA, including turboprops.
It was for a Citation CJ2+
The dual FMS is a moderately rare fit, but they have done a few for european ops.
As it happens the Collins Proline 21 is at it’s best with dual FMS, as FMS1 displays on the pilot’s PFD and FMS2 displays on the copilot’s PFD. When ILS approaches are programmed in each side independently auto-tumes the ILS on separate boxes, and sets the inbound course, initially with a dotted pointer which then goes solid as it changes to green needles.
I suppose in that case you have true redundancy and reversionary capability of nav source, AHRS, ADC, and display, and the autopilot can work from either side.
With a single FMS it is possible to display the same data on both sides but that’s not quite the same thing.
I suppose in a 2 crew situation there is no disputing you meet the requirements in 8.4.3 above, as SOPs would suggest you are both monitoring the approach.
OK… this is totally outside my expertise but there could be any number of regs specific to public transport ops that need GPS (i.e. BRNAV or anything beyond).
I know for example the most modern heavy jets (that actually have GPS!) have three of them, all feeding the INS. Whereas a single bit of DME/DME hardware would do the job, somebody decided they need three GPSs…
For AOC ops, the national CAA can lay down whatever requirements it likes – or certainly could do so in the past.
We are private, but one needs to keep an eye on the future resale into the AOC market; that might have been where it came from. The aircraft is single pilot for private ops and less than 5700kg. And it’s not difficult to fly either.
I know for example the most modern heavy jets (that actually have GPS!) have three of them, all feeding the INS.
You mean “feeding the FMS”? Not all passenger jets have INS, many of the ones that fly shorthaul don’t.
In some hidden place within the smallprint of the operating manual of “my” Citations (550/560) or in the manual of the Honeywell Primus avionics, one can find this little phrase: “Dual FMS installation is required in order to fly RNAV approaces”. Dual FMS would be much more expensive (and almost impossible in terms of available space) to install than dual GPS… So I conculde that a large number of the thousands of Citations out there fly RNAV approches “illegally”. Every day, sometimes seveal every day. Obviouosly the French ramp inspectors have not discovered this part of the manual yet – and hopefully they do not read EuroGA, otherwise I will be an umemployed pilot in the very near future…
Actually I did mean using GPS to correct the INS.
Normally INS is corrected using DME/DME fixups, AFAIK.
An FMS whose position is purely GPS derived is common on light jets (and everything below).
What you say about needing a dual FMS is something else, it seems.
Actually I did mean using GPS to correct the INS.
Normally INS is corrected using DME/DME fixups, AFAIK.
Usually, the FMS is the heart of the navigation system. It is fed coordinates by all attached sensors (DME/DME, also VOR radial/DME, GPS, LORAN, keyboard, INS) and computes a most probable position from all those. This is then fed back to the sensors, that require position updating, like INS. On the ground, there usually are not enough DMEs in range for obtaining a fix – therefore Jeppesen plates 10-9 and following contain exact coordinates of all parking stands for INS initialisation / verification…
Flying the e.g. ILS approach I fly the localizer and glideslope on the autopilot until reaching minima. So, I don’t fly the approach using the synthetic vision. However, the synthetic vision is yet another source to confirm you are on the right track and which will visually help you spot the runway in the right direction and in the right proportion. At reaching the minima I will look for the approach lights mostly below me as with real minima weather I won’t be able to see the runway or its lights yet. The synthetic vision helps me with a 3rd source after the ILS and the visual check of seeing the approach lights.
Now, equipment fails, but then I am not counting and flying visually using only the GPS source to the runway.
Even though taking the wind direction and speed into account and thus knowing approximately where to expect the runway, the synthetic vision makes this so much easier to spot.
