Gulfstream G450

Eddie sez:

Reacting properly to a TCAS resolution advisory can save lives, just look at the cases of C-141 65-9405 and Luftwaffe 74 and DHL 611 and Bashkirian 2937.

Of course, you can argue that it isn't mandatory in the United States. That is technically true but it is mandatory elsewhere in the world. I will let you decide your course of action from the sources below, including the G450 Aircraft Operating Manual, the 14 CFR series, and ICAO Doc 8168, Volume 1.

Me? I follow the RA and let ATC know what I've done.

Everything here is from the references shown below, with a few comments in an alternate color.

Last revision:




[G450 AOM, § 03-08-90]

  1. Initiation of a Resolution Advisory (RA)
  2. Upon initiation of a Resolution Advisory (RA), the pilot flying should focus attention on flying the commanded maneuver. The airplane should be smoothly maneuvered to comply with the TCAS command and to promptly return to ATC clearance when the "CLEAR OF CONFLICT" message is received.

  3. Flight Path Marker and Vertical Pitch Boresight Symbol
  4. During a resolution advisory (RA) the HUD will present a small fly-to-box and provides vertical flight path guidance. Maneuver the flight path marker into this small box. On the PFD during a RA there will be a wider box and vertical pitch boresight symbol provided. Maneuver the pitch boresight symbol (single cue or cross pointer) into this wider box. For Airplanes with ASC 908 and prior, if the HUD cue is in use on the PFD, then it will switch to a single cue pitch reference automatically to provide the proper symbol. Airplanes with ASC 909 and subsequent will retain the HUD cue during an RA. There may also be a FPM displayed on the PFD if FPA is selected on the display controller or for airplanes having ASC 037, when SV-PFD is being used.



  5. Compliance With a TCAS II RA
  6. Compliance with a TCAS II RA is necessary unless the pilot considers it unsafe to do so, or unless the pilot has better information about the cause of the RA and can maintain safe separation (e.g., visual acquisition of, and safe separation from, a nearby airplane, obvious TCAS system failure, etc.)

  7. Flashing TCAS Fly-To-Box
  8. For airplanes having ASC 037 or ASC 037A (or later approved revision), with SV-PFD displayed the TCAS fly-to-box may flash due to “edge limiting”. If this occurs, continue to maneuver into the fly-to-box. It will command the proper escape maneuver.

I like to leave the autopilot engaged to preserve its thought process, including the cleared altitude and course. When the TCAS RA occurs, press and hold the touch control steering button and fly the airplane into the TCAS box. Once "clear of conflict," simply release the touch control steering button and the autopilot will return you to your previously cleared course and altitude.

FAA Procedural Notes

[14 CFR 91, ¶91.123 (c)] Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

[AC 120-55C Air Carrier TCAS Appendix 5]

  1. TCAS RAs. When a flight crew receives a TCAS RA to either climb or descend from their assigned altitude, or the RA otherwise affects their ATC clearance, the crew should inform ATC when beginning the excursion from clearance or as soon as workload allows in the following manner:
    • “XYZ Center, (Aircraft ID), TCAS RA.”
    • Example: “New York Center, Quantum 321, TCAS RA.”
  2. SEPARATION. Following such a communication, the designated air traffic facility is not required to provide approved standard separation to the TCAS maneuvering aircraft until the TCAS encounter is cleared and standard ATC separation is achieved. If workload permits, traffic information should be provided in accordance with the current edition of FAA Order 7110.65, Air Traffic Control. When the RA is clear, the flight crew should advise ATC that they are returning to their previously assigned clearance or subsequent amended clearance in the following manner:
    • “ABC Center, (Aircraft ID), clear of conflict, returning to assigned altitude.”
    • Example: “Boston Center, Northern 429, clear of conflict, returning to assigned altitude.”


[49 CFR 830, ¶830.5] The operator of any civil aircraft, or any public aircraft not operated by the Armed Forces or an intelligence agency of the United States, or any foreign aircraft shall immediately, and by the most expeditious means available, notify the nearest National Transportation Safety Board (NTSB) office, when:

(10) Airborne Collision and Avoidance System (ACAS) resolution advisories issued when an aircraft is being operated on an instrument flight rules flight plan and compliance with the advisory is necessary to avert a substantial risk of collision between two or more aircraft.

So how do you notify the NTSB about a TCAS event? They have an email address set up to do just that:

SVS Symbology


[G450 AOM, § 2B-06-90]

  • Unless Enhanced SVS is installed, the display of TCAS targets (traffic), HSI half-range arc and digits, top down terrain (EGPWS image), weather radar images, and all associated readouts are inhibited on the SV PFD. The HSI auto pop-up logic that exists with the 2/3 PFD and Enhanced SVS, with respect to terrain/traffic alerts, is inhibited when operating with Standard SVS.
  • For aircraft certification Foxtrot and earlier, when a TCAS RA is active and the FD CMD mode is HUD, the boresight symbol is changed to a solid single-cue aircraft symbol, and the flight director and flight path marker, if displayed, are removed.
  • For aircraft certification Golf, when a TCAS RA is active and the FD CMD mode is HUD, the boresight symbol remains the same (no longer changes to single-cue) and flight path-based guidance (same as VGS) is provided during an RA.
  • When a TCAS RA is active and the FD CMD mode is SC, the aircraft symbol changes to a solid single-cue aircraft symbol, and the flight director and flight path marker, if displayed, are removed.
  • When a TCAS RA is active, and the FD CMD mode is CP, the aircraft symbol is changed to a solid cross-pointer aircraft symbol, and the flight director and flight path marker, if displayed, are removed.
  • Red do-not-fly goal posts and a green fly-to rectangle are displayed as on the standard PlaneView PFD. The aircraft symbol is red and solid when in the do-not-fly pitch area. When the aircraft symbol is in the green fly-to rectangle, the aircraft symbol is depicted in green and solid.

HUD Symbology


[G450 AOM, § 2B-18-20 ¶2.D.]

  • The HUD system displays RAs that are generated by the TCAS. These RA commands are translated into FPA commands that are displayed on the HUD.
  • Corrective RAs are displayed as an avoidance zone and fly-to-zone. Preventive RAs are displayed as an avoidance zone. If a corrective RA is displayed, the pilot must maneuver the aircraft until the FPV moves out of the avoidance zone and into the fly-to-zone. If a preventive RA is displayed, the pilot must maintain the current FPA and ensure that the FPV remains out of the avoidance zone.
  • The Clear mode is automatically activated when a TCAS RA is generated.

Flying the flight path vector into the TCAS box in the HUD will keep you safe but it may not keep your right seat pilot happy. If you are climbing, placing the flight path vector in the top of the TCAS box will keep the right seat display green. If you are descending, placing the flight path vector in the bottom of the TCAS box will keep the right seat display green.

Do you have to follow an RA (even when contrary to ATC)?

FAA: Maybe

[14 CFR 91, §91.123]

(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.

(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

(d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall submit a detailed report of that emergency within 48 hours to the manager of that ATC facility, if requested by ATC.

(e) Unless otherwise authorized by ATC, no person operating an aircraft may operate that aircraft according to any clearance or instruction that has been issued to the pilot of another aircraft for radar air traffic control purposes.

The CFR does not require you follow the TCAS RA.

[AIM, ¶ 4-4-16 (as of Feb 9, 2012]

  1. TCAS I provides proximity warning only, to assist the pilot in the visual acquisition of intruder aircraft. No recommended avoidance maneuvers are provided nor authorized as a direct result of a TCAS I warning. It is intended for use by smaller commuter aircraft holding 10 to 30 passenger seats, and general aviation aircraft.
  2. TCAS II provides traffic advisories (TAs) and resolution advisories (RAs). Resolution advisories provide recommended maneuvers in a vertical direction (climb or descend only) to avoid conflicting traffic. Airline aircraft, and larger commuter and business aircraft holding 31 passenger seats or more, use TCAS II equipment.
    1. Each pilot who deviates from an ATC clearance in response to a TCAS II RA must notify ATC of that deviation as soon as practicable and expeditiously return to the current ATC clearance when the traffic conflict is resolved.
    2. Deviations from rules, policies, or clearances should be kept to the minimum necessary to satisfy a TCAS II RA.
    3. The serving IFR air traffic facility is not responsible to provide approved standard IFR separation to an aircraft after a TCAS II RA maneuver until one of the following conditions exists:
    4. (a) The aircraft has returned to its assigned altitude and course.

      (b) Alternate ATC instructions have been issued.

  3. TCAS does not alter or diminish the pilot’s basic authority and responsibility to ensure safe flight. Since TCAS does not respond to aircraft which are not transponder equipped or aircraft with a transponder failure, TCAS alone does not ensure safe separation in every case.
  4. At this time, no air traffic service nor handling is predicated on the availability of TCAS equipment in the aircraft.


[ICAO Doc 8168, Volume 1, §3.2]

c) in the event of an RA, pilots shall:

1) respond immediately by following the RA as indicated, unless doing so would jeopardize the safety of the aeroplane;

Note 1.— Stall warning, wind shear, and ground proximity warning system alerts have precedence over ACAS.

Note 2.— Visually acquired traffic may not be the same traffic causing an RA. Visual perception of an encounter may be misleading, particularly at night.

2) follow the RA even if there is a conflict between the RA and an air traffic control (ATC) instruction to manoeuvre;

3) not manoeuvre in the opposite sense to an RA;

Note.— In the case of an ACAS-ACAS coordinated encounter, the RAs complement each other in order to reduce the potential for collision. Manoeuvres, or lack of manoeuvres, that result in vertical rates opposite to the sense of an RA could result in a collision with the threat aircraft.

4) as soon as possible, as permitted by flight crew workload, notify the appropriate ATC unit of the RA, including the direction of any deviation from the current ATC instruction or clearance;

Note.— Unless informed by the pilot, ATC does not know when ACAS issues RAs. It is possible for ATC to issue instructions that are unknowingly contrary to ACAS RA indications. Therefore, it is important that ATC be notified when an ATC instruction or clearance is not being followed because it conflicts with an RA.

5) promptly comply with any modified RAs;

6) limit the alterations of the flight path to the minimum extent necessary to comply with the RAs;

7) promptly return to the terms of the ATC instruction or clearance when the conflict is resolved; and

8) notify ATC when returning to the current clearance.

14 CFR 91, Title 14: Aeronautics and Space, General Operating and Flight Rules, Federal Aviation Administration, Department of Transportation

49 CFR 830, Title 49: Transportation, National Transportation Safety Board

AC 120-55C Air Carrier TCAS, 2/23/11U.S. Department of Transportation

Aeronautical Information Manual

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.