New Garmin GI-275 install, I want it to display knots!

[ElisiumNate]

Hey Mooney Fam! I'm just about to get started with a replacement of the vacuum system and associated gauges in my '64E.  The GI-275 installer tells me that they have to set the instrument up to show whatever the POH indicates.  My POH is barely legible, and doesn't contain many of the things that current POHs contain. It does describe some speeds in MPH though, and my current airspeed indicator is marked for both. What are the magic words I need to say to them in order to get the instrument set to read knots? 

Thanks! 

[Hank]

My understanding is that your primary indicators need to match your Owners Manual; if that's not legible, grab one from the Downloads section here.

If your Manual says that your gear speed is 120 mph like mine, how many knots is that on your airspeed indicator? Its when your airspeed indicator reads 120 mph. (Yes, I know your 64 E has a different and lower Vg than my 70 C, but I don't know what any of your numbers are, and you don't know how many knots any of them are.)

You can still have your GPS read knots if you want, but your primaries have to match your aircraft documentation. 

If I'm wrong, someone will correct me shortly . . . .

[PT20J]

I believe the STC requires the airspeed units to match the AFM and/or placards.

[Utah20Gflyer]

You would need a 2nd STC that allows for the conversion and would include a revision of the owners manual converting all the old numbers to knots.  
 

Ultimately does it really matter?  You fly the plane by the numbers.  Seems immaterial if those numbers represent statute miles or knots?  

[PeteMc]

6 hours ago, ElisiumNate said:

The GI-275 installer tells me that they have to set the instrument up to show whatever the POH indicates. 

Does your POH show both?  My K manual shows both "XXXmph (XXXkts)" so years ago when I needed to get my ASI worked on I checked with the FSDO and they said it was fine to have it changed to knots since my POH shows both. 

[TaildraggerPilot]

I’m pretty sure that any new/modern indicators need to remain in the units listed in the POH. Type certificate stuff and all……

[varlajo]

9 hours ago, Utah20Gflyer said:

Ultimately does it really matter?  You fly the plane by the numbers.  Seems immaterial if those numbers represent statute miles or knots?  

The only time is does matter is when ATC requests "120 knots or greater" 

[Matthew P]

So, they enter MPH when it's installed, then you go into the 275 and you can choose to display it in MPH or Knots...make sure he gives you the password if he changes it from anything than the default.

[Slick Nick]

So you mean those fancy glass newfangled instruments can’t even display two speeds simultaneously? An old dual-scale ASI has done that for decades. 

[Hank]

Them fancy G5s and Aspens ain't much bigger than a regular ASI, but they cram lots of tiny information onto the screen. Ain't no room for two speeds . . . . (So says this proud owner-operator of a full steam gauge panel!  )

[Slick Nick]

3 hours ago, Hank said:

Them fancy G5s and Aspens ain't much bigger than a regular ASI, but they cram lots of tiny information onto the screen. Ain't no room for two speeds . . . . (So says this proud owner-operator of a full steam gauge panel!  )

Steam gauge fan here also, still gets me where I need to go!

[McMooney]

G5'S in my 74E are in Kts.

[Bob E]

My G5's are also in knots, but two factors tell me that's ok:  (1) the original airspeed indicator shows both MPH and knots, so I had and still have all the info I need regarding MPH.  (2) The Mooney's V-speeds are programmed into the G-5's airspeed ribbon, as pointers rather than numbers when the aircraft is in motion (photos), so knots versus mph isn't relevant. 

 

 

 

[PT20J]

According to the STC installation manual, the instrument units must agree with the units used in the AFM and/or placards. 

If you do otherwise, probably no one will notice, but there is always the chance that some IA will notice it during an annual inspection. If I changed it so that it does not comply with the STC, I’d change it back before I sold it so it would be legal and not potentially cause an issue for the new owner.

 

[Aerodon]

The 'go to' documents for this are the Type Certificate, The Supplemental Type Certificate and the Owners manuals, later called the Pilots Operating Handbook.

The TC list airspeeds in MPH and Knots from 1955 on.  It seems to have everything listed except the stall speed, required to setup your GI-275.  Now it gets a little interesting, prior to 1967 there is no requirement for an Owners Manual, so for all intents, whatever you have is an 'information manual' and use it or not at your own discretion.  (Sure I would like to have the performance charts matching the ASI units).

Then Note 2 lists the Placards, it is very specific, somewhere in the middle of M20J/K production Mooney changed from MPH to Knots. The Placards are very specific, with speeds listed in MPH, but if you had new ones made in MPH (KTS) showing both, I think they would still be acceptable.

So because your plane is prior to 1967, I think the installer can use the speeds in Knots, redo the placards to show MPH and Knots.

I do not know what stall speeds (with and without flaps) to use, other than converting from your old ASI?

Aerodon

 

[Bob E]

My '65 M20C of course has an owner's manual rather than a POH, but it definitely also has an "F.A.A. APPROVED AIRPLANE FLIGHT MANUAL" (approved Oct. 20, 1961 for my specific aircraft serial number by H.H. Slaughter, Chief, Engineering and Manufacturing Branch, Federal Aviation Agency, Southwest Region). It lists all V-speeds as miles per hour of CALIBRATED AIRSPEED.  But the "units," whether CAS, IAS, or TAS, are still in mph. So I think PT20J is right.  

But he's also right that no one will notice. I've had several AIs, CFIs, and DFEs as passengers, and some have flown left seat. No one mentioned anything about mph/knots on the G5s.  (They mostly just complimented me on a nice panel!) I'm sure they know as well as I do that as a practical matter, reprogramming the digital displays to show MPH rather than knots would reduce safety:  ATC speaks in knots, charts are in nautical miles, plates show elapsed time numbers for airspeeds in knots, etc. The risk of enforcement action on this one is basically zero. I'd be interested if ANYONE has a G5 or similar programmed in MPH, and if so what their reasons are for doing so. 

[65MooneyPilot]

When I first setup my G5 I thought I would try knots. I did not take long for me to change it to MPH. When I flew large Boeings I was taught to cross check instruments. So it started to drive me crazy when the speeds were not the same. When I fly now the two instruments are very close which my cross check likes. Yes you could look at the inner knots to cross check but after flying the Mooney for over 30 years on the MPH scale I did not want to reinvent the wheel. If ATC assigns a speed to me then I can look at the inner scale. I don’t fly much IFR anymore to have to think about what speed I am flying. I keep below 250 knots under 10K. Not the greatest picture but the airspeed matches.

[Matthew P]

5 hours ago, Bob E said:

My '65 M20C of course has an owner's manual rather than a POH, but it definitely also has an "F.A.A. APPROVED AIRPLANE FLIGHT MANUAL" (approved Oct. 20, 1961 for my specific aircraft serial number by H.H. Slaughter, Chief, Engineering and Manufacturing Branch, Federal Aviation Agency, Southwest Region). It lists all V-speeds as miles per hour of CALIBRATED AIRSPEED.  But the "units," whether CAS, IAS, or TAS, are still in mph. So I think PT20J is right.  

But he's also right that no one will notice. I've had several AIs, CFIs, and DFEs as passengers, and some have flown left seat. No one mentioned anything about mph/knots on the G5s.  (They mostly just complimented me on a nice panel!) I'm sure they know as well as I do that as a practical matter, reprogramming the digital displays to show MPH rather than knots would reduce safety:  ATC speaks in knots, charts are in nautical miles, plates show elapsed time numbers for airspeeds in knots, etc. The risk of enforcement action on this one is basically zero. I'd be interested if ANYONE has a G5 or similar programmed in MPH, and if so what their reasons are for doing so. 

It doesn't really matter because there is a function that allows you to display in either mph or kts,  on my panel, I shave an airspeed limitations placard that shows both mph/kts...at any given time I can go into my 275 and choose to display whatever I want, if I'm vfr, mph or ifr, kts.. BUT, along with the 275s I still have the original Airspeed Indicator as well...so since I still have the original ASI, it's a mo

Edited Friday at 10:05 AM by Matthew P

[PT20J]

The STC references the AFM and placards, not the POH or Owners Manual. The AFM is required by CAR 3 3.777 and includes the operating limitations. The TCDS will list the applicable AFM. The AFM usually has less information than a POH. The documents may be combined. For example, in my M20J, the limitations section of the POH comprises the AFM and is approved by the FAA as noted in the page footers.

[bigmo]

I've not fooled with the 275 setup before, but do you have an option to display TAS as well (assuming it has a temp feed)? On my AV-30C, the STC is the same, my IAS is configured in MPH as required, but the TAS can be in knots. It's a nice feature to have.

[Matthew P]

14 hours ago, bigmo said:

I've not fooled with the 275 setup before, but do you have an option to display TAS as well (assuming it has a temp feed)? On my AV-30C, the STC is the same, my IAS is configured in MPH as required, but the TAS can be in knots. It's a nice feature to have.

Yes, you have a few things you can display, TAS is just one of them

[Jim Peace]

I just go by wind noise and vibration. Seems to work well enough.