RNP capability in comanche

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tango4
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Joined: 28 Aug 2013, 04:18
Location: Paris, France

RNP capability in comanche

Post by tango4 »

Hi guys,
I have a quick question.
With the Garmin GTN750xi equipped in the Comanche, given the capabilities (or its lack of capabilities) of the autopilot, (No approach mode so no vertical guidance, no GPSS, no FD), is it legal to fly an RNP approach in the Comanche ?
If so, can you do it with LNAV minima only ?
I can't seem to find an answer to that. And could it be different between FAA/EASA ?

Any input appreciated.

Charles MOULIN
Charles MOULIN

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AKar
A2A Master Mechanic
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Joined: 26 May 2013, 05:03

Re: RNP capability in comanche

Post by AKar »

tango4 wrote: 19 Jan 2025, 12:06 With the Garmin GTN750xi equipped in the Comanche, given the capabilities (or its lack of capabilities) of the autopilot, (No approach mode so no vertical guidance, no GPSS, no FD), is it legal to fly an RNP approach in the Comanche ?
If so, can you do it with LNAV minima only ?
I can't seem to find an answer to that. And could it be different between FAA/EASA ?
Hi Charles,

the lack of autopilot (at all, or given capabilities thereof) is not what limits you from being RNP capable, and the GTN 750 series can be approved down to LPV (though individual installations can vary). You can think it is basically the GNSS equivalent for the ILS. Note that some approaches may have different minima when flight director, autopilot, and/or HUD is not used down to DA.

What you can't do are "RNP AR" approaches. At least TDS's simulation correctly models these not being available in the database at all; the other available simulation of somewhat relaxed realism apparently has those available for selection. Also, while pretty much covered by that already, anything that says "RF required" (RF being Radius-to-Fix leg type) is out of consideration.

-Esa

tango4
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Posts: 44
Joined: 28 Aug 2013, 04:18
Location: Paris, France

Re: RNP capability in comanche

Post by tango4 »

Thanks a lot for chiming in.
I a pretty familiar with RNP approaches (working as an ATC at LFPG), and the fact that the GTNxi is LPV capable.
My question was really related to the AP part.
At LFPG all our RNP have AP or FD mandatory but due to parallel operations.
For LFPB (for which we manage the approach) the parallel RNP27 has the same requirement but nothing is specified for the RNP07 (which is not parallel).
So what I wondered was if there was any more « generic » requirement at all to be able to fly an RNP approach besides a GPS unit that is RNP approved and feeding the HSI. I was not sure if there was a more « basic » requirement. If I understand you correctly, as it is equipped, the Comanche can fly any RNP approach (LNAV, LNAV/VNAV, or LPV) except RNP-AR and any procedure including RF legs. But depending on the specific approach, it MIGHT be prohibited (as in LFPG) or have different minima. This is correct ?

Best regards.
Charles MOULIN

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AKar
A2A Master Mechanic
Posts: 5537
Joined: 26 May 2013, 05:03

Re: RNP capability in comanche

Post by AKar »

tango4 wrote: 19 Jan 2025, 14:40 So what I wondered was if there was any more « generic » requirement at all to be able to fly an RNP approach besides a GPS unit that is RNP approved and feeding the HSI. I was not sure if there was a more « basic » requirement. If I understand you correctly, as it is equipped, the Comanche can fly any RNP approach (LNAV, LNAV/VNAV, or LPV) except RNP-AR and any procedure including RF legs. But depending on the specific approach, it MIGHT be prohibited (as in LFPG) or have different minima. This is correct ?
Yes, that is correct as far as I am up to speed. I checked the AIP for de Gaulle, and these requirements are specifically given due to "simultaneous operations", they would not apply by default. How they are applied in practice at de Gaulle - you'd certainly be more of an expert than I am!

There are a list of airworthiness requirements that come into having a system such as GTN RNP capable. The GTN 750 on its own meets all of them as far as I can gather, the remaining relate to the installation-specific issues. However, autopilot, FD, FMS, or HUD, would not be needed unless specifically required by the procedure's criteria, either for credit in minima (like at my 'home airport') or to use the procedure in the first place. The latter of which appears to be the case at de Gaulle. From where these specific operational requirements rise, I'd need to refresh myself.

Interesting discussion, btw!

-Esa

tango4
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Posts: 44
Joined: 28 Aug 2013, 04:18
Location: Paris, France

Re: RNP capability in comanche

Post by tango4 »

Thanks a lot for taking the time to answer me !
This is much appreciated.
Charles MOULIN

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