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Would you have two GPSs?

In 2002, Socata offered the TB20/21 with an option of 2 x GNS430, or possibly a GNS430+GNS530.

I am 99% sure only one of them could drive the autopilot – at least there was ever only one “NAV/GPS” switch. Having both capable of driving the AP would have meant a new KFC225 AFMS

Nowadays, with WAAS/EGNOS, you would need two “WAAS grade” GPS antennae which are quite pricey. But that’s only if the 2nd GPS is to be used “officially” for LPV, I would think.

But more to the point, how would people use two GPSs in flight?

The backup (loss of power or the GPS packing up) situation ought to be adequately addressed with a handheld with a DCT function.

Administrator
Shoreham EGKA, United Kingdom

I think a lot of the Cirrii seem to come with two 430w’s as standard – I’ve never quite seen the point, unless Cirrus buys so many of them that they don’t cost that much more than a normal bendix king nav/com.

Personally, I tend to fly with the 430 and a 296, both programmed for the flight, but find that the 296 is a far better VFR device than the 430. If I had a stormscope and tcas overlaid on the 430 display, I’d want to upgrade to the 530, as the small 430 display tends to get a bit cluttered. But I don’t! Yet….

The idea is probably that for IFR flying, you need to have 2 COM and 2 NAV (VOR/LOC/GS) devices. Partly for redundancy, but also to make transits from one segment of an IFR approach to the other easier: Fly the current segment (e.g. a VOR radial) on NAV 1, but have NAV 2 already setup for the next segment (e.g. the ILS). So you don’t need to switch frequencies, fiddle with OBS rings and whatnot at a time when the workload is already pretty high.

Obviously you could do this with just one 430 COM/NAV/GPS, plus a traditional COM/NAV as number 2. But that means learning how to program two different boxes. It also means a panel with navigation equipment from different generations, which doesn’t look as good as two identical 430s. Or a 530 and a 430.

So for looks and redundancy alone, I’d go with two 430s. But having said that, I don’t like the relatively long startup time of the 430. I fly a relatively simple aircraft, so my checks after engine start are done within a few seconds. But then I need to sit around for what feels like ages (in reality closer to 30 seconds, probably) for the 430 to run through its own checks, before I can talk to the tower to request taxi clearance. So for that reason it would be nice to have a simple COM box which is ready to receive and transmit as soon as it’s powered on.

The radio on my 430s does work immediately on power on.

EGSC

On mine, too.

Frankfurt (EDFE, EDFZ), Germany

True. But you can’t see what frequency it’s set to until the power-on self test is finished. So you have to set it to the proper frequency before switching it off, and hope nothing funny happens when you switch it on again. My home base gives my my startup clearance on the Delivery frequency, and I need to contact Tower for taxi. So I cannot simply keep the box on one single frequency, but I have to switch frequencies as part of the startup routine.

Now I fully agree that with a bit of thought you can get this to work right, but a mistake is easily made.

Last Edited by BackPacker at 25 Mar 17:01

You don’t need to wait while the GNS430 is powering up. After the initial flash screen, you can use the enter key to quickly pass thru the other startup screens. I recommend you examine the self test screen to verify proper operation of the HSI and OBS pointer, the annunciators, and if you have a GPS, you can validate it on this screen.

KUZA

Oceanic navigation requires the use of two GPS units to be an acceptable navigation source.

KUZA

Dual GNS430’s provide redundancy of GPS, MAP, VOR/ILS, and COM. In my experience, many use the second system as a dedicated map for things such as traffic. There are some times when one unit can’t both display a waypoint of interest while conducting a procedure. Ultimately it is the backup that fully redundant systems provide.

KUZA
I am 99% sure only one of them could drive the autopilot – at least there was ever only one “NAV/GPS” switch. Having both capable of driving the AP would have meant a new KFC225 AFMS…

Nowadays, with WAAS/EGNOS, you would need two “WAAS grade” GPS antennae which are quite pricey. But that’s only if the 2nd GPS is to be used “officially” for LPV, I would think.

The main limitation is the KFC225 has a single HSI. With your Sandel, the Nav source can selected for the autopilot.

The WAAS antenna is part of the purchase price for the GPS and comes with the install kit. Only approved GPS antennas can be used with the STC although some of the early systems have antennas that limit the usability for sole source of IFR navigation in the US (91.205) and the AFMS ends up having similar limitations as a non WAAS GPS. A non WAAS antenna will function, but would not be an acceptable installation on a US certified aircraft.

KUZA
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