experience with "side screen ovht" Hawker 900 XP?

[HermanTheGerman]

Hi guys,

we are experiencing this fault now for probably the 3rd time in a row, B panel was exchanged many times, electrical circuit was checked many times, but it is coming again.

It is always the right B panel, the 3rd (aft) of the 3 heating elements is cold. side scrn ovht always coming on short final.

Anybody having any idea what the problem could be? I believe we are going to the wrong maintenance facility (service center).

[vodka_gorbachev]

If you're staying in Berlin, I would strongly recommend Nuremberg or Zurich.

[Woodruf]

What electrical troubleshooting has been carried out? Have you swapped the thermal controllers left and right? Also the control relays in the Da panel.
What voltage do you see at the B screen, can you reproduce the fault on the ground? It sounds like you are losing a phase.


Regards
Woodruf

[deefer dog]

Yep, Berlin and fixing that problem will never appear in the same sentence!

[HermanTheGerman]

thx woodruf, but I have no idea if they changed anything r/l. I am just the stupid pilot- according to RTS they only changed the B panel.

according to a mail they measured the temp-sensor which showed high resistance value so they exchanged the B panel- after that they found everything normal.

If they did anything else, especially since this fault is coming again and again, I have no idea.

[Woodruf]

Herman. I trust you're not being charged for this! If you need any advice as to what to ask about trouble shooting, always happy to help.

[ginopino]

Go to Chester....

[HawkerBeech1]

Herman- Screen overheat can be tricky. First I would like to ask if you have isolated the screen in question. I know you said the RH "B" panel is not heating in all three sections and apparently this can be seen visually correct?. Of course this means this is likely the side with the issue. However...did you confirm this by shutting off windscreen heat one side at a time to see if the side screen light goes out and which switch was responsible? Just curious.
I believe on the 900xp the LH screen heat switch controls the RH side screen heat. Im sure you are looking into the correct side but the more ways you confirm this the better.

Second....ensure that the next tech that works this confirms with a meter that he has correct voltage on all three legs of the RH sidescreen. I believe it will be around 115VAC on each leg. This should only be checked at the "B" screen terminals initially. And do not use a test light. A good, calibrated meter must be used to read exact voltage.

The Hawker "B"screens have 3 separate heating panels with separate power going to each. The three legs are separate all the way from the AC GCU if I remember right. So its not as if there is one power leg to the "B" screen and then it is jumped at the window from leg to leg. Three separate power legs emanating from the rear of the aircraft that run to three separate power terminals on the "B" screen. Also in the window is 2 heat sensors. I believe one sensor is the normal sensor that cycles the heat under normal circumstances. The other sensor is to detect an "overheat" condition and turns on the side screen overheat annunciator. The overheat sensor activates a few degrees above the normal sensor. Both of these sensors are in their own panel. In other words....three separate panels...panel "X" has the normal sensor, panel "Y" has the overheat sensor, and panel "Z" has no sensor at all. This configuration can lead to a unique scenario. If you have no power on the leg that goes to panel "X" that has the normal sensor internal to it...that specific panel never heats up. However the other two panels are getting power and heat normally. But with panel "X" not heating the normal sensor never cycles the controller as it should because that panel does not get hot. The result is panel "Y" and panel "Z" continue to heat up until the overheat sensor in panel "Y" reaches its limit. You then get the side screen overheat light...and you notice on panel "X" of the "B" screen is fogged over.

So check the voltage on all three legs at the suspected "B" screen. What they may see if one leg is out would be a reading as follows.
Leg "X"- 115VAC
Leg "Y"- 115VAC
Leg "Z"- 65 VAC or 0 VAC

If you get 65VAC you actually have no input voltage at Z. Due to the nature of the three legs voltage will backfeed from the other two legs to give this reading of half voltage.

If you confirm this to be the case. Check your breakers behind the copilots left shoulder. Be sure to push them all because they can be tricky. If those are in there is another set of breakers in the rear bay. If I remember..they are directly FWD while standing in the rear bay looking FWD under the green cover. But have the techs confirm this with a diagram. If this are good they will need to check down the line to see where power is lost on that leg.


This is one scenario.

Other possibilities could be:

1) solid state relays malfunction
2) screen heat controller malfunction
3) wiring issues
4) AC GCU

Please be aware that "A" screen controllers and "B" screen controllers are not interchangeable. They control the temps and overheat parameters at differing values. We sometimes see them swapped.

9 times out of 10 the issue is generally inside the window. But we check the entire system out. We do this because even if you find a window that is out of specs....it may well be another failed components that caused that window to be out of specs or damaged. Replacing just the window will simply lead to the replacement window quickly being damaged as well. I will say that most Mx facilities learn this the hard way. And windows aren't cheap.

[HawkerBeech1]

And yes I would recommend Chester. This is not an issue that any ole Mx facility can work. I would also suggest that you insist the techs consult with Tech Support during the troubeshooting procedures. Please provide the techs with the history as well. Including detailed paperwork for previous troubleshooting.

[HermanTheGerman]

thx, HB1, very nice post, thank you very much.

well in short final (less than a mile) we don't have time to switch and identify the screen, but when my copilot touches the screen it is very easy to find out which one of the heating elements is cold.

It is always right B panel, aft heating element.

In flight we don't have a side screen ovht light, but I am 100% sure that on our next flights this heating element will be cold again, when we start taxying in the morning with some water on the screen, I will take a picture and the fault can be clearly identified.

Our maintenance mgr is already working on different places- I am really unhappy, I don't know what to tell the owner this time. We are on support+, so it has to be a Service Center.

[HawkerBeech1]

Yeah...I figured that may be the case.

Just an FYI. If you can confirm on taxi out that the same panel is not heating....write that up on your descrepency in addition to side screen overheat.

** RH "B" screen aft panel does not heat as well as side screen overheat on final (repeat sqk)**

This should force the techs to comply with a thorough ops check of all three panels. After changing a window we generally check for voltage at the terminals as well as physically get on a ladder with engines running and feel for heat on all three sections prior to releasing the AC.

Support Plus is paying off though :ok:

[HermanTheGerman]

HB1 you are a mind-reader. We almost used exactly the same wording in our reports and in our communication with them. At least 2 times.

I will report the outcome of this. Thanks.

[RFGN]

I am sorry to say that: but avoid LBG!
We have had misadventure on a 900XP.

[HawkerBeech1]

Good luck Herman. And please insist that Hawker Tech support be used. Get the name of that particular tech rep as well. That way...if it continues you can use him as your source for all further troubleshooting no matter who does it. At that point technicians play a secondary role and the continuity of troubleshooting remains with the tech rep. And because it is Support Plus...the tech reps should be intimately involved anyways as they are supposed to approve all high cost items like windows to ensure the trouble shooting is correct. HBS is wasting their own money at this point. But your time is another matter.