Transponder Testing/Commissioning

[skippydiesel]

When my new transponder was tested, the technician checked, amongst other things,  speed accuracy -  in a real world sense (probably not bureaucratic) is this as good as doing repeated varying speed runs, to test air speed indicator accuracy?

[RFguy]

test the ASI ? sounds like he was trying to bill extra hours. unless your aircraft was (over) due for testing as normally required is it every 2 years for a RAaus ?

 

 

and no need to test the GPS, is is guaranteed to be accurate by its certification. (again might be a test). There is a CASA instrument that stipulates what needs to be tested after what changes are made, I will have a look at it, others might know.

 

[old man emu]

An airspeed indicator is not an accurate instrument in the way that an altimeter is.  It is tested for accuracy at an air pressure of 1013 hPa and an air temperature of 15C  Those conditions are virtually never met in practice. 

 

True airspeed is used for navigational and aircraft performance purposes. Just think of the factors that you must consider when converting from IAS to TAS. True airspeed or TAS  is defined as “the airspeed of an aircraft relative to undisturbed air.  True airspeed is a calculated airspeed which has been adjusted for both altitude and non-standard air. True Air Speed (TAS) is calculated from Indicated Air Speed (IAS), your Altitude, local QNH and OAT.

[skippydiesel]

4 hours ago, RFguy said:

test the ASI ? sounds like he was trying to bill extra hours. unless your aircraft was (over) due for testing as normally required is it every 2 years for a RAaus ?

 

 

and no need to test the GPS, is is guaranteed to be accurate by its certification. (again might be a test). There is a CASA instrument that stipulates what needs to be tested after what changes are made, I will have a look at it, others might know.

 

May have put it badly - CASA approved transponder test/initialisation (brand new Mode S  transponder) - part of test was to compare calibrated air sped (provided by test equipment) with aircrafts Dynon reading. Technician went through my expected air speeds,  (from stall to above MAX Cruse) - noted expected variation (most instrument have a relatively  accurate reporting band, with progressive inaccuracies the further(+/-)  from the band the readings are). He stated that the Dynon readings were well within the allowable variation ie normal.

 

My question is - will the transponder initialisation air speed readings be acceptable to the powers that be rather than going through a tedious series of flights over a known course /distance/time.

[RFguy]

How did they generate calibrated airspeed- some sort of transducer/ jig applied to the tubes or was inferred by flying ?
I dont think this is necessary - since the aircraft will have its own CAS-IAS  chart for its airspeed readout, and this is an independent system.
That is a LAME/L2 job every two years in RAAUS I thought . 

As for checking if the GPS in the transponder was reading correctly- that's a load of crap IMO,  use of a TSO 199 GPS means it will not readout errors without displaying an error flag- IE the GPS system in those  is self aware of errors and checking.  

https://www.icao.int/APAC/Meetings/2015 ADSBSITF14/SP08b_FAA TABS briefing.pdf

 

TSO-C199 Requirements
• Cannot transmit false or misleading
information
• SDA=1 (1x10-3 or better)
• NACp=9 (30 meters or better)
• NACv=1 (10 m/s or better)
• NIC=6 (0.5 NM or better)
• SIL=1 (1x10-3 or better)
• Detect Step errors greater than 700 meters
• Capable of using SBAS integrity 

 

 

 

 

 

 

Edited April 29, 2023 by RFguy

[Thruster88]

I think Skippy used the term "calibrated airspeed" to mean the box connected to the aircraft pitot tube was calibrated, not CAS you find in a POH.

[RFguy]

ahhhh. right....

I cant see how a machine test can emulate  flying conditions, given the way the airspeed is 'collected' , and all the variabilities.  Flying up and down a course is not too demanding....

 

Edited April 29, 2023 by RFguy

[skippydiesel]

59 minutes ago, RFguy said:

ahhhh. right....

I cant see how a machine test can emulate  flying conditions, given the way the airspeed is 'collected' , and all the variabilities.  Flying up and down a course is not too demanding....

 

Maaate! , have you checked out the  RAA "Flight Test Guide For Amateur Built Recreational Aircraft" - its 37 pages of testing charts/instructions. Any reduction in the number of tests required will be a blessing

 

If I already have a set of figures ( air speed) provided by a recognised third party (CASA) using calibrated test equipment, why would I want to spend time on generating an alternative set, using even an less precise measurement system (stop watch, ground markers, eyesight) with the multitude of variables that impacts on the result(s) ???????????

[facthunter]

The usual Mode c transponder only gets an altitude readout check If I recall correctly. When you call at or prior to CTA entry you give your level and that must accord with the level your transponder indicates and be inside the allowable error.   You may also be given an individual CODE to further identify you. This only works in radar  COVERAGE.  Nev

[PapaFox]

A ground based pitot-static check will verify the accuracy of the altimeter and vsi instrument but not the full installation. If you are sensing static pressure in a poor location aerodynamically, your readings will not be indicating accurately. 

[skippydiesel]

6 hours ago, facthunter said:

The usual Mode c transponder only gets an altitude readout check If I recall correctly. When you call at or prior to CTA entry you give your level and that must accord with the level your transponder indicates and be inside the allowable error.   You may also be given an individual CODE to further identify you. This only works in radar  COVERAGE.  Nev

Mine is a Mode S - ID/speed/altitude/heading

[skippydiesel]

2 hours ago, PapaFox said:

A ground based pitot-static check will verify the accuracy of the altimeter and vsi instrument but not the full installation. If you are sensing static pressure in a poor location aerodynamically, your readings will not be indicating accurately. 

You are correct however my static port is located directly below the pitot (part of the same assembly) so I would not expect there to be a significant change from the ground test results. Further my Dynon also reports TAS & Ground Speed which are GPS generated - the combined level of accuracy is already well beyond the old steam gauges, the testing seems to be written around

Edited April 30, 2023 by skippydiesel