# In support of removal of periodic calibration of Flight Recorders

Innovation | Electromobility | Automation | Human Factors
Mar. 24, 2023

### In support of removal of periodic calibration of Flight Recorders

1. IGC PLENARY 2023 PROPOSAL 6.1.1 Reno Filla on behalf of the proponents DENMARK + FRANCE hopefully not completely “technically illiterate”
2. The impact of an error in measuring air pressure on the measured altitude value is not constant but varies with altitude
3. The Barometric Formula https://en.wikipedia.org/wiki/Barometric_formula Δℎ Δ𝑝𝑝 ≠ const
4. The Barometric Formula https://en.wikipedia.org/wiki/Barometric_formula Example:
5. Assessing errors in pressure measurement Input: Altitude Pressure at sea level Output: Pressure at altitude Input: Pressure measurement error Output: Altitude with error Example for offset error:
6. Assessing errors in pressure measurement Input: Altitude Pressure at sea level Output: Pressure at altitude Input: Pressure measurement error Output: Altitude with error Example for gain error:
7. Assessing errors in pressure measurement
8. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m)
9. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa
10. -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 True altitude (m) Altitude error (m) -1 hPa +1 hPa
11. -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa
12. -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa
13. True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 -1 hPa +1 hPa -3 hPa +3 hPa -1 % +1 % 0
14. -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -1 % +1 %
15. -300 -200 -100 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 0 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -1 % +1 %
16. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m)
17. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) ? 1% of the pressure value or 1% of the altitude value according to 2011 spec
18. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa
19. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa
20. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -10 hPa +10 hPa With SPAC Without correction
21. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -10 hPa +10 hPa With SPAC
22. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 hPa +1 hPa -3 hPa +3 hPa -10 hPa +10 hPa
23. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m)
24. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 % +1 %
25. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 % +1 % -2 % +2 %
26. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -1 % +1 % -2 % +2 % -3 % +3 % With SPAC Without correction
27. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) +3 % -3 % +6 % -6 % With SPAC
28. -300 -200 -100 0 100 200 300 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) +3 % -3 % +6 % -6 %
29. https://www.stssensors.com/blog/2020/06/30/the-long-term-stability-of-pressure-sensors/ From opposing position paper, section 3.1 SPAC Surface Pressure Altitude Correction • ±3 hPa (offset error) • ±3 % (gain error) within acceptable accuracy beyond 10000 m • ±10 hPa (offset error) • ±6 % (gain error) within acceptable accuracy up to 6000 m They advocate SPAC! ±6 hPa (offset error) ±5 % (gain error) ±8 hPa (offset error) ±5 % (gain error)
30. SPAC Surface Pressure Altitude Correction • ±3 hPa (offset error) • ±3 % (gain error) within acceptable accuracy beyond 10000 m • ±10 hPa (offset error) • ±6 % (gain error) within acceptable accuracy up to 6000 m https://www.stssensors.com/blog/2020/06/30/the-long-term-stability-of-pressure-sensors/ From opposing position paper, section 3.2 ±6 hPa (offset error) ±5 % (gain error) ±8 hPa (offset error) ±5 % (gain error)
31. SPAC Surface Pressure Altitude Correction • ±3 hPa (offset error) • ±3 % (gain error) within acceptable accuracy beyond 10000 m • ±10 hPa (offset error) • ±6 % (gain error) within acceptable accuracy up to 6000 m https://www.amsys-sensor.com/downloads/data/MS5607-02BA03-AMSYS-datasheet.pdf Looks OK! ±6 hPa (offset error) ±5 % (gain error) ±8 hPa (offset error) ±5 % (gain error)
32. SPAC Surface Pressure Altitude Correction • ±3 hPa (offset error) • ±3 % (gain error) within acceptable accuracy beyond 10000 m • ±10 hPa (offset error) • ±6 % (gain error) within acceptable accuracy up to 6000 m Competitions: • Maximum Start Altitude: 1000-2000 m • Minimum Finish Altitude: 400-600 m • Contest Area Altitude Limit: < 3000 m Silver badge: • Loss of Height: 1000 m • Height gain: 1000 m Gold badge: • Loss of Height: 1000 m • Height gain: 3000 m Diamonds: • Loss of Height: 1000 m • Height gain: 5000 m Distance diplomas: • Loss of Height: 1000 m Conclusion: Are all comfortably covered with SPAC No need for mandatory periodic calibration Not covered: Altitude records (typical > 10000m) (internationally now requiring HAFR) ±6 hPa (offset error) ±5 % (gain error) ±8 hPa (offset error) ±5 % (gain error)
33. Detecting a possibly degraded pressure sensor in need of service Requirements on any method: • Simple (no need for fancy tools and programs, perhaps assisted by a website) • Robust and clear indication • Should not require a cooperating pilot • If possible avoid requirement for cooperative OO (for example registering current QNH) • Enable verification in retrospect, using only the igc file • If possible avoid the need to look up QNH from an online database (example: Copernicus) Thoughts: • GPS Altitude is quite good given sufficient SIU* and FXA** values • NOT of interest: the absolute difference between GPS Altitude and Pressure Altitude in a single fix • VERY MUCH of interest: the overall correlation of GPS Altitude and Pressure Altitude in a time window • Noise exists in all signals and there are statistical means to deal with it • A linear regression of Pressure Altitude over GPS Altitude ideally results in a slope=1 → perfect correlation without gain error • We don’t need to know QNH but we need to ensure that it doesn’t change • Solution: only use the first x minutes after launch, when the glider hasn’t moved much in (lat, long) • This also makes calculation of the local geoid height unnecessary *) SIU = Satellites In Use **) FXA = Fix Accuracy (expressed as Estimated Position Error)
34. Detecting a possibly degraded pressure sensor in need of service Example: Only use fixes from the following section • first 30 minutes after launch • only 3D fixes • only fixes with SIU ≥ 8 • only fixes with FXA ≤ 20 m *) SIU = Satellites In Use **) FXA = Fix Accuracy (expressed as Estimated Position Error) slope: 1.007 intercept: -99.2 r_value: 0.99945 p_value: 0.0 std_err: 0.00085 ≈1: PA correlates very well with GPS Altitude = no gain error R2 ≈1: almost 100% of PA explained by GPS Altitude + offset offset due to QNH ≠ STD (or offset error, we don’t know) (offset error will be first revealed at higher altitudes or if we know the QNH) ((subtracting geoid height not necessary given sufficiently short time window)) p ≈ 0: statistically highly significant correlation between GPS Altitude and PA (this is not just random noise) std deviation ≈ 0: very little spread around the centerline Conclusion: No sign of degraded pressure sensor in this FR – no need for service
35. Detecting a possibly degraded pressure sensor in need of service Example: Only use fixes from the following section • first 30 minutes after launch • only 3D fixes • only fixes with SIU ≥ 8 • only fixes with FXA ≤ 20 m *) SIU = Satellites In Use **) FXA = Fix Accuracy (expressed as Estimated Position Error) slope: 1.007 intercept: -99.2 r_value: 0.99945 p_value: 0.0 std_err: 0.00085 ≈1: PA correlates very well with GPS Altitude = no gain error Question: What if an ”unlucky combination” of offset error and gain error yields a perfectly linear relationship between PA and GPS Alt? Example: -8 hPa offset error & -6 % gain error
36. -800 -600 -400 -200 0 200 400 600 800 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) +8 hPa, -6 % -8 hPa, +6 % -8 hPa, -6 % +8 hPa, +6 % With SPAC Without correction
37. -800 -600 -400 -200 0 200 400 600 800 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 True altitude (m) Altitude error (m) -8 hPa, -6 % +8 hPa, +6 % With SPAC Question: What if an ”unlucky combination” of offset error and gain error yields a near-perfect linear relationship between PA and GPS Alt.? Answer: It will also yield a near-perfect SPAC correction → not a problem! +8 hPa, -6 % -8 hPa, +6 %