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// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// interactive.c: aircraft tracking and interactive display
//
// Copyright (c) 2014,2015 Oliver Jowett <oliver@mutability.co.uk>
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
// This file incorporates work covered by the following copyright and
// permission notice:
//
// Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "dump1090.h"
//
// ============================= Utility functions ==========================
//
static uint64_t mstime(void) {
struct timeval tv;
uint64_t mst;
gettimeofday(&tv, NULL);
mst = ((uint64_t)tv.tv_sec)*1000;
mst += tv.tv_usec/1000;
return mst;
}
//
//========================= Interactive mode ===============================
//
// Return a new aircraft structure for the interactive mode linked list
// of aircraft
//
struct aircraft *interactiveCreateAircraft(struct modesMessage *mm) {
static struct aircraft zeroAircraft;
struct aircraft *a = (struct aircraft *) malloc(sizeof(*a));
int i;
// Default everything to zero/NULL
*a = zeroAircraft;
// Now initialise things that should not be 0/NULL to their defaults
a->addr = mm->addr;
for (i = 0; i < 8; ++i)
a->signalLevel[i] = mm->signalLevel; // First time, initialise everything
// to the first signal strength
// mm->msgtype 32 is used to represent Mode A/C. These values can never change, so
// set them once here during initialisation, and don't bother to set them every
// time this ModeA/C is received again in the future
if (mm->msgtype == 32) {
int modeC = ModeAToModeC(mm->modeA | mm->fs);
a->modeACflags = MODEAC_MSG_FLAG;
if (modeC < -12) {
a->modeACflags |= MODEAC_MSG_MODEA_ONLY;
} else {
mm->altitude = modeC * 100;
mm->bFlags |= MODES_ACFLAGS_ALTITUDE_VALID;
}
}
return (a);
}
//
//=========================================================================
//
// Return the aircraft with the specified address, or NULL if no aircraft
// exists with this address.
//
struct aircraft *interactiveFindAircraft(uint32_t addr) {
struct aircraft *a = Modes.aircrafts;
while(a) {
if (a->addr == addr) return (a);
a = a->next;
}
return (NULL);
}
//
//=========================================================================
//
// We have received a Mode A or C response.
//
// Search through the list of known Mode-S aircraft and tag them if this Mode A/C
// matches their known Mode S Squawks or Altitudes(+/- 50feet).
//
// A Mode S equipped aircraft may also respond to Mode A and Mode C SSR interrogations.
// We can't tell if this is a Mode A or C, so scan through the entire aircraft list
// looking for matches on Mode A (squawk) and Mode C (altitude). Flag in the Mode S
// records that we have had a potential Mode A or Mode C response from this aircraft.
//
// If an aircraft responds to Mode A then it's highly likely to be responding to mode C
// too, and vice verca. Therefore, once the mode S record is tagged with both a Mode A
// and a Mode C flag, we can be fairly confident that this Mode A/C frame relates to that
// Mode S aircraft.
//
// Mode C's are more likely to clash than Mode A's; There could be several aircraft
// cruising at FL370, but it's less likely (though not impossible) that there are two
// aircraft on the same squawk. Therefore, give precidence to Mode A record matches
//
// Note : It's theoretically possible for an aircraft to have the same value for Mode A
// and Mode C. Therefore we have to check BOTH A AND C for EVERY S.
//
void interactiveUpdateAircraftModeA(struct aircraft *a) {
struct aircraft *b = Modes.aircrafts;
while(b) {
if ((b->modeACflags & MODEAC_MSG_FLAG) == 0) {// skip any fudged ICAO records
// If both (a) and (b) have valid squawks...
if ((a->bFlags & b->bFlags) & MODES_ACFLAGS_SQUAWK_VALID) {
// ...check for Mode-A == Mode-S Squawk matches
if (a->modeA == b->modeA) { // If a 'real' Mode-S ICAO exists using this Mode-A Squawk
b->modeAcount = a->messages;
b->modeACflags |= MODEAC_MSG_MODEA_HIT;
a->modeACflags |= MODEAC_MSG_MODEA_HIT;
if ( (b->modeAcount > 0) &&
( (b->modeCcount > 1)
|| (a->modeACflags & MODEAC_MSG_MODEA_ONLY)) ) // Allow Mode-A only matches if this Mode-A is invalid Mode-C
{a->modeACflags |= MODEAC_MSG_MODES_HIT;} // flag this ModeA/C probably belongs to a known Mode S
}
}
// If both (a) and (b) have valid altitudes...
if ((a->bFlags & b->bFlags) & MODES_ACFLAGS_ALTITUDE_VALID) {
// ... check for Mode-C == Mode-S Altitude matches
if ( (a->modeC == b->modeC ) // If a 'real' Mode-S ICAO exists at this Mode-C Altitude
|| (a->modeC == b->modeC + 1) // or this Mode-C - 100 ft
|| (a->modeC + 1 == b->modeC ) ) { // or this Mode-C + 100 ft
b->modeCcount = a->messages;
b->modeACflags |= MODEAC_MSG_MODEC_HIT;
a->modeACflags |= MODEAC_MSG_MODEC_HIT;
if ( (b->modeAcount > 0) &&
(b->modeCcount > 1) )
{a->modeACflags |= (MODEAC_MSG_MODES_HIT | MODEAC_MSG_MODEC_OLD);} // flag this ModeA/C probably belongs to a known Mode S
}
}
}
b = b->next;
}
}
//
//=========================================================================
//
void interactiveUpdateAircraftModeS() {
struct aircraft *a = Modes.aircrafts;
while(a) {
int flags = a->modeACflags;
if (flags & MODEAC_MSG_FLAG) { // find any fudged ICAO records
// clear the current A,C and S hit bits ready for this attempt
a->modeACflags = flags & ~(MODEAC_MSG_MODEA_HIT | MODEAC_MSG_MODEC_HIT | MODEAC_MSG_MODES_HIT);
interactiveUpdateAircraftModeA(a); // and attempt to match them with Mode-S
}
a = a->next;
}
}
//
//=========================================================================
//
// Receive new messages and populate the interactive mode with more info
//
// Distance between points on a spherical earth.
// This has up to 0.5% error because the earth isn't actually spherical
// (but we don't use it in situations where that matters)
static double greatcircle(double lat0, double lon0, double lat1, double lon1)
{
lat0 = lat0 * M_PI / 180.0;
lon0 = lon0 * M_PI / 180.0;
lat1 = lat1 * M_PI / 180.0;
lon1 = lon1 * M_PI / 180.0;
return 6371e3 * acos(sin(lat0) * sin(lat1) + cos(lat0) * cos(lat1) * cos(fabs(lon0 - lon1)));
}
static int doGlobalCPR(struct aircraft *a, int fflag, int surface)
{
int result;
double lat=0, lon=0;
if (surface) {
// surface global CPR
// find reference location
double reflat, reflon;
if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK) { // Ok to try aircraft relative first
reflat = a->lat;
reflon = a->lon;
} else if (Modes.bUserFlags & MODES_USER_LATLON_VALID) {
reflat = Modes.fUserLat;
reflon = Modes.fUserLon;
} else {
// No local reference, give up
return (-1);
}
result = decodeCPRsurface(reflat, reflon,
a->even_cprlat, a->even_cprlon,
a->odd_cprlat, a->odd_cprlon,
fflag,
&lat, &lon);
} else {
// airborne global CPR
result = decodeCPRairborne(a->even_cprlat, a->even_cprlon,
a->odd_cprlat, a->odd_cprlon,
fflag,
&lat, &lon);
}
if (result < 0)
return result;
// check max range
if (Modes.maxRange > 0 && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) {
double range = greatcircle(Modes.fUserLat, Modes.fUserLon, lat, lon);
if (range > Modes.maxRange)
return (-2); // we consider an out-of-range value to be bad data
}
a->lat = lat;
a->lon = lon;
return 0;
}
static int doLocalCPR(struct aircraft *a, int fflag, int surface, time_t now)
{
// relative CPR
// find reference location
double reflat, reflon, lat=0, lon=0;
double range_limit = 0;
int result;
if (a->bFlags & MODES_ACFLAGS_LATLON_REL_OK) {
int elapsed = (int)(now - a->seenLatLon);
if (elapsed < 0) elapsed = 0;
reflat = a->lat;
reflon = a->lon;
// impose a range limit based on 2000km/h speed
range_limit = 5e3 + (2000e3 * elapsed / 3600); // 5km + 2000km/h
} else if (!surface && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) {
reflat = Modes.fUserLat;
reflon = Modes.fUserLon;
// The cell size is at least 360NM, giving a nominal
// max range of 180NM (half a cell).
//
// If the receiver range is more than half a cell
// then we must limit this range further to avoid
// ambiguity. (e.g. if we receive a position report
// at 200NM distance, this may resolve to a position
// at (200-360) = 160NM in the wrong direction)
if (Modes.maxRange > 1852*180)
range_limit = (1852*360) - Modes.maxRange;
} else {
// No local reference, give up
return (-1);
}
result = decodeCPRrelative(reflat, reflon,
fflag ? a->odd_cprlat : a->even_cprlat,
fflag ? a->odd_cprlon : a->even_cprlon,
fflag, surface,
&lat, &lon);
if (result < 0)
return result;
// check range limit
if (range_limit > 0) {
double range = greatcircle(reflat, reflon, lat, lon);
if (range > range_limit)
return (-1);
}
// check max range
if (Modes.maxRange > 0 && (Modes.bUserFlags & MODES_USER_LATLON_VALID)) {
double range = greatcircle(Modes.fUserLat, Modes.fUserLon, lat, lon);
if (range > Modes.maxRange)
return (-2); // we consider an out-of-range value to be bad data
}
a->lat = lat;
a->lon = lon;
return 0;
}
static void updatePosition(struct aircraft *a, struct modesMessage *mm, time_t now)
{
int location_result = -1;
if (mm->bFlags & MODES_ACFLAGS_LLODD_VALID) {
a->odd_cprlat = mm->raw_latitude;
a->odd_cprlon = mm->raw_longitude;
a->odd_cprtime = mstime();
} else {
a->even_cprlat = mm->raw_latitude;
a->even_cprlon = mm->raw_longitude;
a->even_cprtime = mstime();
}
// If we have enough recent data, try global CPR
if (((mm->bFlags | a->bFlags) & MODES_ACFLAGS_LLEITHER_VALID) == MODES_ACFLAGS_LLBOTH_VALID && abs((int)(a->even_cprtime - a->odd_cprtime)) <= 10000) {
location_result = doGlobalCPR(a, (mm->bFlags & MODES_ACFLAGS_LLODD_VALID), (mm->bFlags & MODES_ACFLAGS_AOG));
if (location_result == -2) {
// Global CPR failed because an airborne position produced implausible results.
// This is bad data. Discard both odd and even messages and wait for a fresh pair.
// Also disable aircraft-relative positions until we have a new good position (but don't discard the
// recorded position itself)
Modes.stats_current.cpr_global_bad++;
mm->bFlags &= ~(MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID);
a->bFlags &= ~(MODES_ACFLAGS_LATLON_REL_OK | MODES_ACFLAGS_LLODD_VALID | MODES_ACFLAGS_LLEVEN_VALID);
return;
} else if (location_result == -1) {
// No local reference for surface position available, or the two messages crossed a zone.
// Nonfatal, try again later.
Modes.stats_current.cpr_global_skipped++;
} else {
Modes.stats_current.cpr_global_ok++;
}
}
// Otherwise try relative CPR.
if (location_result == -1) {
location_result = doLocalCPR(a, (mm->bFlags & MODES_ACFLAGS_LLODD_VALID), (mm->bFlags & MODES_ACFLAGS_AOG), now);
if (location_result == -1) {
Modes.stats_current.cpr_local_skipped++;
} else {
Modes.stats_current.cpr_local_ok++;
mm->bFlags |= MODES_ACFLAGS_REL_CPR_USED;
}
}
if (location_result == 0) {
// If we sucessfully decoded, back copy the results to mm so that we can print them in list output
mm->bFlags |= MODES_ACFLAGS_LATLON_VALID;
mm->fLat = a->lat;
mm->fLon = a->lon;
// Update aircraft state
a->bFlags |= (MODES_ACFLAGS_LATLON_VALID | MODES_ACFLAGS_LATLON_REL_OK);
a->seenLatLon = a->seen;
a->timestampLatLon = a->timestamp;
}
}
struct aircraft *interactiveReceiveData(struct modesMessage *mm) {
struct aircraft *a, *aux;
time_t now = time(NULL);
// Lookup our aircraft or create a new one
a = interactiveFindAircraft(mm->addr);
if (!a) { // If it's a currently unknown aircraft....
a = interactiveCreateAircraft(mm); // ., create a new record for it,
a->next = Modes.aircrafts; // .. and put it at the head of the list
Modes.aircrafts = a;
} else {
/* If it is an already known aircraft, move it on head
* so we keep aircrafts ordered by received message time.
*
* However move it on head only if at least one second elapsed
* since the aircraft that is currently on head sent a message,
* othewise with multiple aircrafts at the same time we have an
* useless shuffle of positions on the screen. */
if (0 && Modes.aircrafts != a && (now - a->seen) >= 1) {
aux = Modes.aircrafts;
while(aux->next != a) aux = aux->next;
/* Now we are a node before the aircraft to remove. */
aux->next = aux->next->next; /* removed. */
/* Add on head */
a->next = Modes.aircrafts;
Modes.aircrafts = a;
}
}
a->signalLevel[a->messages & 7] = mm->signalLevel;// replace the 8th oldest signal strength
a->seen = now;
a->timestamp = mm->timestampMsg;
a->messages++;
// If a (new) CALLSIGN has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_CALLSIGN_VALID) {
memcpy(a->flight, mm->flight, sizeof(a->flight));
}
// If a (new) ALTITUDE has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_ALTITUDE_VALID) {
if ( (a->modeCcount) // if we've a modeCcount already
&& (a->altitude != mm->altitude ) ) // and Altitude has changed
// && (a->modeC != mm->modeC + 1) // and Altitude not changed by +100 feet
// && (a->modeC + 1 != mm->modeC ) ) // and Altitude not changes by -100 feet
{
a->modeCcount = 0; //....zero the hit count
a->modeACflags &= ~MODEAC_MSG_MODEC_HIT;
}
a->altitude = mm->altitude;
a->modeC = (mm->altitude + 49) / 100;
}
// If a (new) SQUAWK has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_SQUAWK_VALID) {
if (a->modeA != mm->modeA) {
a->modeAcount = 0; // Squawk has changed, so zero the hit count
a->modeACflags &= ~MODEAC_MSG_MODEA_HIT;
}
a->modeA = mm->modeA;
}
// If a (new) HEADING has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_HEADING_VALID) {
a->track = mm->heading;
}
// If a (new) SPEED has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_SPEED_VALID) {
a->speed = mm->velocity;
}
// If a (new) Vertical Descent rate has been received, copy it to the aircraft structure
if (mm->bFlags & MODES_ACFLAGS_VERTRATE_VALID) {
a->vert_rate = mm->vert_rate;
}
// if the Aircraft has landed or taken off since the last message, clear the even/odd CPR flags
if ((mm->bFlags & MODES_ACFLAGS_AOG_VALID) && ((a->bFlags ^ mm->bFlags) & MODES_ACFLAGS_AOG)) {
a->bFlags &= ~(MODES_ACFLAGS_LLBOTH_VALID | MODES_ACFLAGS_AOG);
}
// If we've got a new cprlat or cprlon
if (mm->bFlags & MODES_ACFLAGS_LLEITHER_VALID) {
updatePosition(a, mm, now);
}
// Update the aircrafts a->bFlags to reflect the newly received mm->bFlags;
a->bFlags |= mm->bFlags;
if (mm->msgtype == 32) {
int flags = a->modeACflags;
if ((flags & (MODEAC_MSG_MODEC_HIT | MODEAC_MSG_MODEC_OLD)) == MODEAC_MSG_MODEC_OLD) {
//
// This Mode-C doesn't currently hit any known Mode-S, but it used to because MODEAC_MSG_MODEC_OLD is
// set So the aircraft it used to match has either changed altitude, or gone out of our receiver range
//
// We've now received this Mode-A/C again, so it must be a new aircraft. It could be another aircraft
// at the same Mode-C altitude, or it could be a new airctraft with a new Mods-A squawk.
//
// To avoid masking this aircraft from the interactive display, clear the MODEAC_MSG_MODES_OLD flag
// and set messages to 1;
//
a->modeACflags = flags & ~MODEAC_MSG_MODEC_OLD;
a->messages = 1;
}
}
return (a);
}
//
//=========================================================================
//
// Show the currently captured interactive data on screen.
//
void interactiveShowData(void) {
struct aircraft *a = Modes.aircrafts;
time_t now = time(NULL);
int count = 0;
char progress;
char spinner[4] = "|/-\\";
// Refresh screen every (MODES_INTERACTIVE_REFRESH_TIME) miliseconde
if ((mstime() - Modes.interactive_last_update) < MODES_INTERACTIVE_REFRESH_TIME)
{return;}
Modes.interactive_last_update = mstime();
// Attempt to reconsile any ModeA/C with known Mode-S
// We can't condition on Modes.modeac because ModeA/C could be comming
// in from a raw input port which we can't turn off.
interactiveUpdateAircraftModeS();
progress = spinner[time(NULL)%4];
#ifndef _WIN32
printf("\x1b[H\x1b[2J"); // Clear the screen
#else
cls();
#endif
if (Modes.interactive_rtl1090 == 0) {
printf (
"Hex Mode Sqwk Flight Alt Spd Hdg Lat Long RSSI Msgs Ti%c\n", progress);
} else {
printf (
"Hex Flight Alt V/S GS TT SSR G*456^ Msgs Seen %c\n", progress);
}
printf(
"-------------------------------------------------------------------------------\n");
while(a && (count < Modes.interactive_rows)) {
if ((now - a->seen) < Modes.interactive_display_ttl)
{
int msgs = a->messages;
int flags = a->modeACflags;
if ( (((flags & (MODEAC_MSG_FLAG )) == 0 ) )
|| (((flags & (MODEAC_MSG_MODES_HIT | MODEAC_MSG_MODEA_ONLY)) == MODEAC_MSG_MODEA_ONLY) && (msgs > 4 ) )
|| (((flags & (MODEAC_MSG_MODES_HIT | MODEAC_MSG_MODEC_OLD )) == 0 ) && (msgs > 127) )
) {
int altitude = a->altitude, speed = a->speed;
char strSquawk[5] = " ";
char strFl[6] = " ";
char strTt[5] = " ";
char strGs[5] = " ";
// Convert units to metric if --metric was specified
if (Modes.metric) {
altitude = (int) (altitude / 3.2828);
speed = (int) (speed * 1.852);
}
if (a->bFlags & MODES_ACFLAGS_SQUAWK_VALID) {
snprintf(strSquawk,5,"%04x", a->modeA);}
if (a->bFlags & MODES_ACFLAGS_SPEED_VALID) {
snprintf (strGs, 5,"%3d", speed);}
if (a->bFlags & MODES_ACFLAGS_HEADING_VALID) {
snprintf (strTt, 5,"%03d", a->track);}
if (msgs > 99999) {
msgs = 99999;}
if (Modes.interactive_rtl1090) { // RTL1090 display mode
if (a->bFlags & MODES_ACFLAGS_ALTITUDE_VALID) {
snprintf(strFl,6,"F%03d",(altitude/100));
}
printf("%06x %-8s %-4s %-3s %-3s %4s %-6d %-2d\n",
a->addr, a->flight, strFl, strGs, strTt, strSquawk, msgs, (int)(now - a->seen));
} else { // Dump1090 display mode
char strMode[5] = " ";
char strLat[8] = " ";
char strLon[9] = " ";
double * pSig = a->signalLevel;
double signalAverage = (pSig[0] + pSig[1] + pSig[2] + pSig[3] +
pSig[4] + pSig[5] + pSig[6] + pSig[7]) / 8.0;
if ((flags & MODEAC_MSG_FLAG) == 0) {
strMode[0] = 'S';
} else if (flags & MODEAC_MSG_MODEA_ONLY) {
strMode[0] = 'A';
}
if (flags & MODEAC_MSG_MODEA_HIT) {strMode[2] = 'a';}
if (flags & MODEAC_MSG_MODEC_HIT) {strMode[3] = 'c';}
if (a->bFlags & MODES_ACFLAGS_LATLON_VALID) {
snprintf(strLat, 8,"%7.03f", a->lat);
snprintf(strLon, 9,"%8.03f", a->lon);
}
if (a->bFlags & MODES_ACFLAGS_AOG) {
snprintf(strFl, 6," grnd");
} else if (a->bFlags & MODES_ACFLAGS_ALTITUDE_VALID) {
snprintf(strFl, 6, "%5d", altitude);
}
printf("%06X%s %-4s %-4s %-8s %5s %3s %3s %7s %8s %5.1f %5d %2d\n",
a->addr, (a->bFlags & MODES_ACFLAGS_NON_ICAO) ? "~" : " ",
strMode, strSquawk, a->flight, strFl, strGs, strTt,
strLat, strLon, 10 * log10(signalAverage), msgs, (int)(now - a->seen));
}
count++;
}
}
a = a->next;
}
}
//
//=========================================================================
//
// When in interactive mode If we don't receive new nessages within
// MODES_INTERACTIVE_DELETE_TTL seconds we remove the aircraft from the list.
//
void interactiveRemoveStaleAircrafts(void) {
struct aircraft *a = Modes.aircrafts;
struct aircraft *prev = NULL;
time_t now = time(NULL);
// Only do cleanup once per second
if (Modes.last_cleanup_time != now) {
Modes.last_cleanup_time = now;
while(a) {
if ((now - a->seen) > Modes.interactive_delete_ttl) {
// Remove the element from the linked list, with care
// if we are removing the first element
if (!prev) {
Modes.aircrafts = a->next; free(a); a = Modes.aircrafts;
} else {
prev->next = a->next; free(a); a = prev->next;
}
} else {
prev = a; a = a->next;
}
}
}
}
//
//=========================================================================
//
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