Skip to content

comm_b: penalise BDS 6,0 candidates whose IAS and Mach disagree at th… #149

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
wiedehopf merged 1 commit into from
Sep 22, 2026
Merged

comm_b: penalise BDS 6,0 candidates whose IAS and Mach disagree at th… #149

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 18 additions & 1 deletion comm_b.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -779,7 +779,24 @@ static int decodeBDS60(struct modesMessage *mm, bool store) {

// small penalty for inconsistent data

// Should check IAS vs Mach at given altitude, but the maths is a little involved
// IAS vs Mach consistency at the pressure altitude carried by DF20 (ISA, CAS ~ IAS).
// A BDS 5,0 misclassified as 6,0 (or bit errors) fails this even when every
// field is individually within range.
if (ias_valid && mach_valid && mm->baro_alt_valid && mm->baro_alt_unit == UNIT_FEET
&& mm->baro_alt > -1500 && mm->baro_alt < 60000) {
double h_m = mm->baro_alt * 0.3048;
double p_ratio;
if (h_m <= 11000.0) {
p_ratio = pow(1.0 - 2.25577e-5 * h_m, 5.25588);
} else {
p_ratio = 0.22336 * exp(-(h_m - 11000.0) / 6341.62);
}
double qc_p0 = p_ratio * (pow(1.0 + 0.2 * mach * mach, 3.5) - 1.0);
double cas = 661.47 * sqrt(5.0 * (pow(qc_p0 + 1.0, 2.0 / 7.0) - 1.0));
if (fabs(cas - (double) ias) > 25.0) {
score -= 12;
}
}

if (baro_rate_valid && inertial_rate_valid) {
int delta = abs(baro_rate - inertial_rate);
Expand Down