Why isn’t my flight compartment window heating?

Modified on Sun, 15 Dec, 2024 at 3:11 PM

Your Hawker flight compartment window isn’t heating, here are some things that could be the issue:

Double check, are the switches, (alternator and windshield heat) in the ON position?
Are the circuit breakers on the DA-D panel closed?
What about the 6 “magnetic” circuit breakers on the DA-B panel, right behind the co-pilot seat?

Our usual thought is that the failure is the window, either the A or B screen. While those are definitely expensive, and could be the fault, maybe it’s not actually the window. We’ll look at some of those other faults below.
In the last quarter of 2024, the window availability has become much better than just a year ago, and we can help you locate a replacement, or used ones to avoid.
Not just one manufacturer of the windows. There are PMA and STC replacements available. There are three different part numbers you could order for each of the A screens, and two different part numbers for each of the B screens.

It could be a controller issue.
The A screen controllers can be swapped with each other and the B screen controllers can be swapped with each other, however you should never swap the A to B, or B to A controllers.
How do I read the numbers on the controller Terminals? The terminal boards on the controller only have the numbers 1 through 5. Those terminals are located to the right side of that terminal board and numbers 6 through 10 are located to the left side of the terminal board.
The terminals are very fragile and can break off due to over torquing or placing a side load on the terminal.
We find that about 20% of heating issues are due to a faulty controller.
In the last quarter of 2024, controllers have been hard to find. Hopefully new controllers will be available again soon.
In the last quarter of 2024, controllers have been hard to find. Hopefully new controllers will be available again soon.

That screen overheat annunciator on the means that for some reason, the normal control of the window temperature isn’t working correctly.
The screen should still heat up, but now at a higher temperature than the normal control should limit it to. The problem with this is that it is shortening the life of your window. If there was any chance of not having to replace the window, the longer you operate it going into the overheat condition, the quicker it is going to fail.

Magnetic circuit breakers behind the co-pilot seat that overheat could be the problem.
These circuit breakers seem to be the weakest link in the electrical circuit. Textron Aviation issued some service information on what to look for on these overheating problems. We have seen breakers overheated again just two years after installing new ones.
If you have a window failure, you should inspect these circuit breakers before installing a replacement.
If you have overheated breakers, you should inspect the terminal boards M on the GG panel to ensure that it hasn’t had any overheating issues.

The controllers output power to the normal and overheat relays.
The normal relays job is to turn the heat on and off to regulate the temperature.
Those A screen normal relays are high speed, solid state relays. You probably hear them buzzing inside the DA panel. They can be a little difficult to troubleshoot as they don’t operate completely like typical relays.
Those solid sate relays can fail in the open or closed condition.
Part numbers of the solid state relays have changed a couple of times now. We can help you identify the correct part number to install.

AC power for the windows comes from the two engine driven alternators.
If one fails, (or it’s electrical circuit fails) load shedding will drop the B screens and only power up the A screens.
When the aircraft goes airborne (conditions apply) the windows will heat at an even higher temperature.

Four switches on the DA-B panel, behind the co-pilot seat, perform some testing on the A and B screen windows.
While all conditions met to make the windows heat on the ground, manipulating each of the four switches to the up and down position will test out parts of the window and controller.

AeroDiagnose can provide Technical Assistance and Ground Support Equipment (for sale or rental) to help you troubleshoot your Hawker flight compartment heated windows.