The image is extracted from this Airbus A350 video (at 3m40s, when taking off)enter image description here

I circled in purple the strange pattern formed by few black straight lines. I'm quite puzzled as I have no idea of what it is or what purpose it can serve.

EDIT: I would like to sum up the ideas in comments as there is interesting guess and discussions in the comments. It is a strange device which can be:

  • a kind of gauge useful as the windscreen seems to be a completely new one and the aircraft presented is one of the test aircraft
  • part of some windscreen heating device
  • 12
    $\begingroup$ looks like electric windscreen heat to me, but I'll defer to someone with specific systems knowledge of this airplane. $\endgroup$
    – casey
    Aug 25, 2015 at 13:46
  • 2
    $\begingroup$ @ManuH It doesn't need to cover more area. I don't know the a350 but it is almost identical to other screen heaters I've seen. Those things get really hot, they will burn you hand, and the windscreen only needs to be a little above freezing. $\endgroup$
    – Simon
    Aug 25, 2015 at 17:58
  • 3
    $\begingroup$ @Simon Ah, so you don't need to be an SR-71 pilot to be able to warm your lunch on the windshield! (As long as you choose the right part of it.) $\endgroup$ Aug 25, 2015 at 19:15
  • 12
    $\begingroup$ Darn, I was really hoping it was the cockpit glass detonation cord for the A350 ejection seat. :-) $\endgroup$
    – RoboKaren
    Aug 26, 2015 at 3:07
  • 2
    $\begingroup$ @casey I agree with you. They are not heating elements as some others have suggested, but rather an electrical bus which provides electricity to a conductive windshield which heats the entire thing. I'm not familiar with the specific aircraft, but there are three sets, which probably are for something like high, low, and emergency settings for the windshield heat. $\endgroup$
    – Lnafziger
    Aug 27, 2015 at 3:17

1 Answer 1


Short answer

These are the three redundant temperature sensors for the windscreen anti icing and defogging system. The design is similar to what is found on the A330 and A340, and most large aircraft. The sensors are used to control the electric current in the heating film(s) sandwiched in the windscreen ply. Usually three temperatures are monitored:

  • Outer windscreen layer must be above freezing point, e.g. 1.8°C.
  • Film mustn't overheat, depends on film used.
  • Inner layer must be below some threshold, e.g. 50°C.

This video shows how windscreen heating works on an ATR42. Extract related to the sensors:

ATR42 windscreen temperature sensors and film bus bars
ATR42 windscreen temperature sensors and film bus bars

The heating film(s) is/are used both to prevent icing and failure of the outer panel (air temperature can be as low as -60°C) and fogging on the inner panel. This can be obtain using a single film, but sometimes there are two distinct films:

Structure of the windscreen on a Boeing 787
Structure of the windscreen on a Boeing 787. Source

On the A350

From A-350 Technical Training Manual:

enter image description here

Windows Anti Icing/Defogging Function, Description and Interfaces

The windows anti icing/defogging system is divided into two sub-systems (F/O and CAPT). Each sub-system is comprised of one windshield, one FWD lateral window, one AFT lateral window and a Window Heat Computer (WHC). [...]

The anti icing and defogging function of the cockpit windshields is ensured by the heating of one resistive/heating film. Each windshield's resistive heating film is powered by 230 VAC, provided by the WHC.

There are three temperature sensors near the heating film that continually send information to the WHC for the heating regulation and the overheat protection functions. [...]

The WHC regulates the temperature of the cockpit windows (35 degrees C to 42 degrees C) based on the temperature value it receives from one of the three temperature sensors. The other two temperature sensors are in standby mode. [...]

If the temperature of the cockpit windows reaches a specific temperature level (+60 degrees C), the WHC will stop supplying the specific window. [...] For each window, the WHC uses temperature values from the three temperature sensors to detect an overheat.

The WHCs interface and exchange data via CRDCs with the AFDX network.The two WHCs are located in the cockpit: WHC1 is located next to the fourth occupant console behind the Captain. WHC2 is located next to the coat stowage behind the First Officer.

For this test aircraft:

  • Sensors are larger than usual.
  • They may be stuck on the glass instead of being built-in.

This setting might be specific for flight test purposes. Someone may bring additional elements.

Another example, on a Pilatus PC12-NG:

Pilatus PC12-NG temperature sensors and bus bars on the windscreen
Pilatus PC12-NG temperature sensors and bus bars on the windscreen

  • $\begingroup$ The inner layer must also be above ambient temperature inside cockpit to prevent the fogging (or at least above dew point, but that's not known). $\endgroup$
    – Jan Hudec
    Apr 21, 2021 at 17:16
  • $\begingroup$ @JanHudec: True, but with a cabin RH of 20% at 20°C, the dew point is below 0°C. So that would be a problem only prior to closing the doors. $\endgroup$
    – mins
    Apr 21, 2021 at 17:26

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