This video shows a 777 engine exhaust through the HUD of a civil aviation aircraft (a comment mentions it's a Gulfstream G650). As it's obvious from the image (screenshot below), the HUD returns thermal information.

What is the purpose of a thermal HUD for a non-military aircraft? Or is it simply a byproduct of the way the HUD works, a thermal image not being its primary purpose?

enter image description here


2 Answers 2


That is a Gulfstream Enhanced Vision System (EVS), also called enhanced flight vision system (EFVS). The HUD shows the usual information (attitude, altitude, airspeed, etc.) and can additionally show the image of a forward-looking infrared (FLIR) camera.

The Gulfstream EVS and later EVS II systems use an IR (infrared) camera mounted in the aircraft's nose to project a raster image on the Heads-Up Display (HUD). The IR image on the HUD is conformal to the outside scene, meaning that objects detected by the IR camera are the same size and aligned with objects outside the aircraft. Thus in poor visibility the pilot is able to view the IR camera image and is able to seamlessly and easily transition to the outside world as the aircraft gets closer to the runway.

The advantage of EVS is that safety in nearly all phases of flight is enhanced, especially during approach and landing in limited visibility. A pilot on a stabilized approach is able to recognize the runway environment (lights, runway markings, etc.) earlier in preparation for touchdown. Obstacles such as terrain, structures, and vehicles or other aircraft on the runway, that might not otherwise be seen, are clearly visible on the IR image.

(SKYbrary - Enhanced Vision System)

The system is not just for night vision, which usually works with visible and near-infrared light. The FLIR uses longer wavelengths because they provide better visibility through mist and fog:

These camera systems can see through smoke, fog, haze, and other atmospheric obscurants better than a visible light camera can.

(Wikipedia: FLIR)

This allows taking off and flying approaches in low visibility with improved situational awareness. An appropriately certified EFVS allows descending below DA (decision altitude) down to 100 ft above the runway since 2004:

EFVS minima
(FAA AC 20-167A)

Since 2017 (FAA AC 90-106A), even EFVS operations below 100 ft including landing and rollout have been approved according to 14 CFR § 91.176 (a). Gulfstream's implementation is certified for landing since 2019.

Related questions:


It's a Head Up Display with an added FLIR feature for seeing in the dark.

  • $\begingroup$ So, if I understand correctly, the main goal is night vision, and the "byproduct" of that is a strong thermal image, correct? $\endgroup$
    – user12873
    Commented Aug 31, 2021 at 4:56
  • 3
    $\begingroup$ @DigitalDracula. In the dark (for our eyes), the only significant radiation is Earth radiative cooling in IR, so this is the band the sensors are optimized for. $\endgroup$
    – mins
    Commented Aug 31, 2021 at 8:26

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