fix(fw_latlon_control): prevent NaN eas2tas from zero-airspeed division - #28107
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mahima-yoga merged 1 commit intoJul 30, 2026
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🔎 FLASH Analysispx4_fmu-v5x [Total VM Diff: 16 byte (0 %)] FILE SIZE VM SIZE
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+0.0% +16 +0.0% +16 .text
+8.2% +16 +8.2% +16 FwLateralLongitudinalControl::updateAirspeed()
+0.0% +55 [ = ] 0 .debug_abbrev
-0.0% -2 [ = ] 0 .debug_info
-0.0% -5 [ = ] 0 .debug_line
+0.0% +5 [ = ] 0 .debug_loclists
-0.0% -1 [ = ] 0 .debug_rnglists
+200% +2 [ = ] 0 [Unmapped]
-0.0% -3 [ = ] 0 [section .debug_rnglists]
-0.2% -16 [ = ] 0 [Unmapped]
+0.0% +52 +0.0% +16 TOTAL
FILE SIZE VM SIZE
-------------- --------------
+0.0% +16 +0.0% +16 .text
+8.2% +16 +8.2% +16 FwLateralLongitudinalControl::updateAirspeed()
+0.0% +55 [ = ] 0 .debug_abbrev
-0.0% -2 [ = ] 0 .debug_info
-0.0% -5 [ = ] 0 .debug_line
-0.0% -4 [ = ] 0 .debug_rnglists
-33.3% -1 [ = ] 0 [Unmapped]
-0.0% -3 [ = ] 0 [section .debug_rnglists]
-0.3% -16 [ = ] 0 [Unmapped]
+0.0% +44 +0.0% +16 TOTAL
Updated: 2026-07-30T10:09:10 |
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July 30, 2026 10:02
sfuhrer
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Jul 30, 2026
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Solved Problem
Before takeoff, if TAS = CAS = 0, the eas2tas conversion computed in the FwLateralLongitudinalControl module becomes NaN. This then results in a NAN TAS, the TECS STE filter doesn't recover from that, and the throttle goes to zero.
Part of the TECS nan propogation issue (the pitch part) was fixed here, but wasn't flown in the above case. Throttle part not addressed yet.
Solution
If CAS < FLT_EPSILON, keep the previous eas2tas.
Changelog Entry
For release notes:
Alternatives
The real solution for all of these cases would be to not allow a NaN measurement into the filter and/or reset it if it does enter. While I do that though, this fixes the immediate issue and I would like to get this in.