diff --git a/sw/airborne/tcas.c b/sw/airborne/tcas.c
new file mode 100644
index 0000000000..2095f35783
--- /dev/null
+++ b/sw/airborne/tcas.c
@@ -0,0 +1,162 @@
+/*
+ * Paparazzi mcu0 $Id$
+ *  
+ * Copyright (C) 2003-2005  Pascal Brisset, Antoine Drouin
+ *
+ * This file is part of paparazzi.
+ *
+ * paparazzi is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * paparazzi 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 paparazzi; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA. 
+ *
+ */
+
+/** \file tcas.c
+ *  \brief Collision avoidance library
+ * 
+ */
+
+#include "tcas.h"
+#include "airframe.h"
+#include "estimator.h"
+#include "nav.h"
+#include "gps.h"
+#include "flight_plan.h"
+
+float tcas_alt_setpoint;
+float tcas_tau_ta, tcas_tau_ra, tcas_dmod, tcas_alim;
+
+uint8_t tcas_status;
+uint8_t tcas_ac_RA;
+uint8_t tcas_acs_status[NB_ACS];
+
+#ifndef TCAS_TAU_TA     // Traffic Advisory
+#define TCAS_TAU_TA 2*CARROT
+#endif
+
+#ifndef TCAS_TAU_RA     // Resolution Advisory
+#define TCAS_TAU_RA CARROT
+#endif
+
+#ifndef TCAS_DMOD       // Distance Modification
+#define TCAS_DMOD 10.
+#endif
+
+#ifndef TCAS_ALIM       // Altitude Limit
+#define TCAS_ALIM 10.
+#endif
+
+#ifndef TCAS_DT_MAX
+#define TCAS_DT_MAX 1500 // ms
+#endif
+
+#define TCAS_HUGE_TAU 100*TCAS_TAU_TA
+
+void tcas_init( void ) {
+  tcas_alt_setpoint = GROUND_ALT + SECURITY_HEIGHT;
+  tcas_tau_ta = TCAS_TAU_TA;
+  tcas_tau_ra = TCAS_TAU_RA;
+  tcas_dmod = TCAS_DMOD;
+  tcas_alim = TCAS_ALIM;
+  tcas_status = TCAS_NO_ALARM;
+  tcas_ac_RA = AC_ID;
+  uint8_t i;
+  for (i = 0; i < NB_ACS; i++) tcas_acs_status[i] = TCAS_NO_ALARM;
+}
+
+
+/* conflicts detection and monitoring */
+void tcas_periodic_task_1Hz( void ) {
+  // test possible conflicts
+  float tau_min = tcas_tau_ta;
+  uint8_t ac_id_close = AC_ID;
+  uint8_t i;
+  float vx = estimator_hspeed_mod * sin(estimator_hspeed_dir);
+  float vy = estimator_hspeed_mod * cos(estimator_hspeed_dir);
+  for (i = 2; i < NB_ACS; i++) {
+    if (the_acs[i].ac_id == 0) continue; // no AC data
+    uint32_t dt = gps_itow - the_acs[i].itow;
+    if (dt > 3*TCAS_DT_MAX) {
+      tcas_acs_status[i] = TCAS_NO_ALARM; // timeout, reset status
+      continue;
+    }
+    if (dt > TCAS_DT_MAX) continue; // lost com but keep current status
+    float dx = the_acs[i].east - estimator_x;
+    float dy = the_acs[i].north - estimator_y;
+    float dz = the_acs[i].alt - estimator_z;
+    float dvx = vx - the_acs[i].gspeed * sin(the_acs[i].course);
+    float dvy = vy - the_acs[i].gspeed * cos(the_acs[i].course);
+    float dvz = estimator_z_dot - the_acs[i].climb;
+    float scal = (dvx*dx + dvy*dy + dvz*dz);
+    float tau = TCAS_HUGE_TAU;
+    if (scal > 0) tau = (dx*dx + dy*dy + dz*dz) / scal;
+    // monitor conflicts
+    switch (tcas_acs_status[i]) {
+      case TCAS_RA:
+        if (tau == TCAS_HUGE_TAU) tcas_acs_status[i] = TCAS_NO_ALARM; // conflict is now resolved
+        break;
+      case TCAS_TA:
+        if (tau < TCAS_TAU_RA) {
+          tcas_acs_status[i] = TCAS_RA; // TA -> RA
+          //TODO Downlink alert
+          break;
+        }
+        if (tau > TCAS_TAU_TA) tcas_acs_status[i] = TCAS_NO_ALARM; // conflict is now resolved
+        break;
+      case TCAS_NO_ALARM:
+        if (tau < TCAS_TAU_TA) {
+          tcas_acs_status[i] = TCAS_TA; // NO_ALARM -> TA
+          //TODO Downlink warning
+        }
+        if (tau < TCAS_TAU_RA) {
+          tcas_acs_status[i] = TCAS_RA; // NO_ALARM -> RA = big problem ?
+          //TODO Downlink alert
+        }
+        break;
+    }
+    // store closest AC
+    if (tau < tau_min) {
+      tau_min = tau;
+      ac_id_close = the_acs[i].ac_id;
+    }
+  }
+  // set current conflict mode
+  if (!(tcas_status == TCAS_RA && tcas_ac_RA != AC_ID && tcas_acs_status[the_acs_id[tcas_ac_RA]] == TCAS_RA)) {
+    tcas_status = tcas_acs_status[the_acs_id[ac_id_close]];
+    if (tcas_status == TCAS_RA) tcas_ac_RA = ac_id_close;
+    else tcas_ac_RA = AC_ID; // no conflicts
+  }
+}
+
+
+/* altitude control loop */
+void tcas_periodic_task_4Hz( void ) {
+  // set alt setpoint
+  if (estimator_z > GROUND_ALT + SECURITY_HEIGHT) {
+    struct ac_info_ * ac = get_ac_info(tcas_ac_RA);
+    float dz = ac->alt - estimator_z;
+    if (dz > tcas_alim) // go up
+      tcas_alt_setpoint = Max(nav_altitude, ac->alt + tcas_alim);
+    if (dz < -tcas_alim) // go down
+      tcas_alt_setpoint = Min(nav_altitude, ac->alt - tcas_alim);
+    else // AC with the smallest ID goes down
+    {
+      if (AC_ID < tcas_ac_RA) tcas_alt_setpoint = Min(nav_altitude, ac->alt - tcas_alim);
+      else tcas_alt_setpoint = Max(nav_altitude, ac->alt + tcas_alim);
+    }
+    // Bound alt
+    tcas_alt_setpoint = Max(GROUND_ALT + SECURITY_HEIGHT, tcas_alt_setpoint);
+  }
+  else tcas_alt_setpoint = nav_altitude;
+}
diff --git a/sw/airborne/tcas.h b/sw/airborne/tcas.h
new file mode 100644
index 0000000000..1798ef7b03
--- /dev/null
+++ b/sw/airborne/tcas.h
@@ -0,0 +1,53 @@
+/*
+ * Paparazzi mcu0 $Id$
+ *  
+ * Copyright (C) 2003-2005  Pascal Brisset, Antoine Drouin
+ *
+ * This file is part of paparazzi.
+ *
+ * paparazzi is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * paparazzi 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 paparazzi; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA. 
+ *
+ */
+
+/** \file tcas.h
+ *  \brief Collision avoidance library
+ * 
+ */
+
+#ifndef TCAS_H
+#define TCAS_H
+
+#include "std.h"
+#include "traffic_info.h"
+
+extern float tcas_alt_setpoint;
+extern float tcas_tau_ta, tcas_tau_ra, tcas_dmod, tcas_alim;
+
+#define TCAS_NO_ALARM 0
+#define TCAS_TA 1
+#define TCAS_RA 2
+extern uint8_t tcas_status;
+extern uint8_t tcas_ac_RA;
+
+extern uint8_t tcas_acs_status[NB_ACS];
+
+extern void tcas_init( void );
+extern void tcas_periodic_task_1Hz( void );
+extern void tcas_periodic_task_4Hz( void );
+
+#define CallTCAS() { if (tcas_status == TCAS_RA) v_ctl_altitude_setpoint = tcas_alt_setpoint; }
+
+#endif // TCAS