Biennial Transponder Check

[DHeal]

Tomorrow I am getting my biennial transponder check at a local avionics shop. This is for my RV-12 ELS (Skyview 10 / ADS-B / VFR-only). I recall somewhere that Dynon describes the appropriate procedure to accomplish this check. Where can I find this procedure?

 

[kellym]

From page 11-43 of the Installation Guide:

"Performing Transponder Checks

Manipulating Altitude:

If the test on your transponder requires manipulating the static pressure, be sure to manipulate static pressure only after activating SkyView’s pitot/static test mode. Instructions for using this mode are in chapter 5 of this manual. Pitot/static test mode is accessed via SETUP MENU > HARDWARE CALIBRATION


The SV-XNDR-261/262 can now be manually switched to ALT and GND modes: XPNDR > ALT and XPNDR > GND."

Note the key instructions are at the end of Chapter 5 of the install manual, page 5-22.
The system MUST be put in static system TEST mode to avoid creating problems with the ADAHRS when it sees vertical movement with no forward movement.
1. The aircraft itself should be temperature stable. For example, if the aircraft is moved from outside in the sun to a hangar for testing, tests should not be started until the airplane has stabilized at the hangar temperature.
2. Turn SkyView on and let it warm up until the altitude reading is stabilized. This period should be at least 5 minutes, but may take longer depending on environmental conditions.
To enter pitot/static test mode, go to:
SETUP MENU > HARDWARE CALIBRATION > ADAHRS CALIBRATION > PITOT STATIC TEST MODE.
Do not fly the aircraft while in pitot/static test mode.
When pitot/static test mode is active, both the active and standby ADAHRS (if equipped) are shown side by side to allow a single test to calibrated multiple ADAHRS. The airspeed and altitude values shown in this mode are the same as you would encounter while in-flight. They are not adjusted or otherwise altered from their normal readings and behaviors.
See related procedure:
SV-XPNDR-261/262 Installation and Configuration, Performing Transponder Checks.

 

[DHeal]

Thanks all -- my avionics tech said he never sees any problems with Dynon equipment.

 

[RVDan]

if you are only doing the transponder check (91.413) and not the static system check for IFR (91.411), there is no need to run the static system up. If you are doing the static system check then as mentioned, make sure the system is in static system test mode. The static system check is only required for IFR.

 

[kellym]

if you are only doing the transponder check (91.413) and not the static system check for IFR (91.411), there is no need to run the static system up. If you are doing the static system check then as mentioned, make sure the system is in static system test mode. The static system check is only required for IFR.

There are two checks that are supposed to be done for VFR that do require checking static system, but only to 1000 above field elevation....a leak check, and correspondence between encoder and altimeter. For Dynon Skyview, the altimeter and encoding use same source, so no issue there, but leak check is still needed.

 

[RVDan]

There are two checks that are supposed to be done for VFR that do require checking static system, but only to 1000 above field elevation....a leak check, and correspondence between encoder and altimeter. For Dynon Skyview, the altimeter and encoding use same source, so no issue there, but leak check is still needed.

The leak check only needs to be done if the system has been broken into. 91.411 applies to IFR only. Over the years some have thought that a leak check is required for all aircraft, but that is not reflected in any rule. It is good practice though to do a leak check if the system is broken into. So, unless the ADAHRS or other aspects of the static lines have been disturbed there is no need for a static check for VFR only aircraft.

 

[kellym]

The leak check only needs to be done if the system has been broken into. 91.411 applies to IFR only. Over the years some have thought that a leak check is required for all aircraft, but that is not reflected in any rule. It is good practice though to do a leak check if the system is broken into. So, unless the ADAHRS or other aspects of the static lines have been disturbed there is no need for a static check for VFR only aircraft.

What you quote applies between biennial checks.
When you are flying in airspace that requires an altitude encoder, whether VFR or IFR controllers and other aircraft are relying on the accuracy of your reported altitude. If you are cleared into Class B airspace, separation is dependent on your reported altitude. I'm not saying altitude needs to be certified to max operating altitude, like IFR, but you do need to know that the system is leak-free, so that your ADAHRS is responding to a real barometric pressure and not some cabin air pressure. One can debate legal requirements, but as a practical matter you need to know you have a leak free system or you may have both airspeed and altitude errors. Over a two year time fittings can loosen, lines can chafe, etc. Especially when the system may be built with non-aircraft grade materials.

 

[RVDan]

What you quote applies between biennial checks.
When you are flying in airspace that requires an altitude encoder, whether VFR or IFR controllers and other aircraft are relying on the accuracy of your reported altitude. If you are cleared into Class B airspace, separation is dependent on your reported altitude. I'm not saying altitude needs to be certified to max operating altitude, like IFR, but you do need to know that the system is leak-free, so that your ADAHRS is responding to a real barometric pressure and not some cabin air pressure. One can debate legal requirements, but as a practical matter you need to know you have a leak free system or you may have both airspeed and altitude errors. Over a two year time fittings can loosen, lines can chafe, etc. Especially when the system may be built with non-aircraft grade materials.

Agreed that we want a system with acceptable leak rates. Lleak checking biannually just because is unnecessary unless the static system plumbing is of poor quality. That is why I stated that best practice is to check whenever the system has been disturbed. Having done the 91.411 and .413 checks as a tech, I can say, that few certified small airplanes have leak free systems. All in all, in unpressurized airplanes the worse case error is small. Consider that most systems with an alternate static source simply vent to the cockpit and the errors are 50 ft or less.

That said, if you have concerns about a system leaking, get it checked out. If the system was leak checked tight and not disturbed it likely is still tight. Same as the plumbing for the rest of the airplane systems.

 

[kellym]

Agreed that we want a system with acceptable leak rates. Lleak checking biannually just because is unnecessary unless the static system plumbing is of poor quality. That is why I stated that best practice is to check whenever the system has been disturbed. Having done the 91.411 and .413 checks as a tech, I can say, that few certified small airplanes have leak free systems. All in all, in unpressurized airplanes the worse case error is small. Consider that most systems with an alternate static source simply vent to the cockpit and the errors are 50 ft or less.

That said, if you have concerns about a system leaking, get it checked out. If the system was leak checked tight and not disturbed it likely is still tight. Same as the plumbing for the rest of the airplane systems.

I respect your experience as a tech. However, in 45 yrs of flying, 35 with IFR certified systems, I can say that many SE Cessnas will not pass a leak check because of the way the port is fastened inside the exterior skin. As a Tech Rep, I see a lot of experimental systems, most without alternate static source, some with static ports not optimized for location, with varying qualities of hose and fittings as well as support for those lines, so the odds of them not leaking are not all that good.
The error in unpressurized planes will depend a lot of the aircraft speed and altitudes flown, and easily can be more than 50 ft if up into the teens in 150kt plus airplane. Do you really want to be 100-200 ft off at altitudes where jets have no speed limits? Where their TCAS is dependent on your reported altitude? A leak check is no harder to do than a mag timing, so why not do it every 2 yrs if not every year? Perhaps not an issue for a light sport aircraft, but most RVs besides the -12 are high performance planes.
Kelly
A&P/IA, EAA Tech Rep