Sat Nov 21, 2020 1:50 pm
#1810102
Given the discussion on Airspace infringements I though the information below (from a post on Gliderpilot.net) might be of interest - especially anyone operating a TMG in a non-gliding environment where the maintenance team might not be so familiar with "Total Energy" probes and their plumbing. Note that it would also be easy to connect the TE line to the Altimeter, with similar errors - the correct connection is of course TE probe to variometer, static to Altimeter/ASI/Transponder.
Something from the latest CHIRP to be aware of:
https://members.gliding.co.uk/2020/11/19/latest-chirp-report/
Report No.4 – Transponder Accuracy
Report Text: I have a hand in maintaining a club motor glider which had a transponder (XPDR) issue; the aircraft in question has a ModeS XPDR. Various pilots reported multiple ATC requests to confirm altitude, with one in particular needing to prove that he had not infringed controlled airspace. There appeared to be a discrepancy of approximately 400ft. I took a flight with one of the reporting pilots and we checked readings with ATC, which appeared to be within limits. Some head-scratching followed as this result did not confirm reports. The issue was subsequently confirmed to me when asking for a transit clearance; the associated check of altitude and pressure setting confirmed approximately 400ft excess altitude being transmitted by the ModeS XPDR in ACS mode with extended squitter - I put the XPDR U/S. I then took to the books and tried to figure out what could be amiss. Eventually it became clear – as a motor-glider, as well as normal Pitot and Static pneumatic connections there is also a Total Energy (T/E) connection. I did the sums for the pressure reduction provided by T/E at the cruise airspeed and this related to about 400 feet! A quick look behind the panel revealed that there were 2 (unmarked) black pneumatic tubes and - yes you have guessed – the T/E was connected to the XPDR and the Static to the variometer (a sensitive rate of climb instrument - T/E is used to remove speed variation indications (stick lift) in gliding so that you only ‘read’ energy gain (or loss)). Problem solved! The tubes are now labelled and will, in due course, be replaced with new colour coded (and labelled) replacements! Unmarked connections of the same type and colour with different functions is not good engineering practice!
Something from the latest CHIRP to be aware of:
https://members.gliding.co.uk/2020/11/19/latest-chirp-report/
Report No.4 – Transponder Accuracy
Report Text: I have a hand in maintaining a club motor glider which had a transponder (XPDR) issue; the aircraft in question has a ModeS XPDR. Various pilots reported multiple ATC requests to confirm altitude, with one in particular needing to prove that he had not infringed controlled airspace. There appeared to be a discrepancy of approximately 400ft. I took a flight with one of the reporting pilots and we checked readings with ATC, which appeared to be within limits. Some head-scratching followed as this result did not confirm reports. The issue was subsequently confirmed to me when asking for a transit clearance; the associated check of altitude and pressure setting confirmed approximately 400ft excess altitude being transmitted by the ModeS XPDR in ACS mode with extended squitter - I put the XPDR U/S. I then took to the books and tried to figure out what could be amiss. Eventually it became clear – as a motor-glider, as well as normal Pitot and Static pneumatic connections there is also a Total Energy (T/E) connection. I did the sums for the pressure reduction provided by T/E at the cruise airspeed and this related to about 400 feet! A quick look behind the panel revealed that there were 2 (unmarked) black pneumatic tubes and - yes you have guessed – the T/E was connected to the XPDR and the Static to the variometer (a sensitive rate of climb instrument - T/E is used to remove speed variation indications (stick lift) in gliding so that you only ‘read’ energy gain (or loss)). Problem solved! The tubes are now labelled and will, in due course, be replaced with new colour coded (and labelled) replacements! Unmarked connections of the same type and colour with different functions is not good engineering practice!