Ice and Rain Protection — Page 257, Lesson 323

We're moving into windscreen protection now, and I want to walk you through the three main ways we keep the pilot's view clear: fluid sprays, electrical heating, and cabin air for demisting. Let's start with the electrical side, because that's the most straightforward. Electrical heating can be built directly into the main windscreen itself, or it can be added as an optional extra. When it's an optional extra, we fit a small heated glass panel in front of the windscreen. That's a separate pane that does the heating job for you. On top of that, some aircraft also have wipers, and those wipers can be assisted by rain repellent systems. So you've got three layers of defence: heat, wipers, and chemical repellent. Now let's talk about the wipers themselves. We call them windshield or windscreen wipers. Independent two-speed wipers are usually provided for both pilots — that means each pilot has their own wiper, and they operate independently of each other. They can be powered either electrically or hydraulically, and they have two operating speeds. Some systems also have a parking facility, which tucks the wiper blade away neatly when you're not using it. Here's a critical operational rule: you should never operate the wipers on a dry windscreen. Running a wiper blade over dry glass causes excessive wear and can scratch the screen, so you always need moisture or washer fluid present. Next, the windscreen washers. This system sprays washer fluid into the windscreen panels, and it's used in conjunction with the wipers to clean the windscreens. So the washer sprays, the wiper wipes — they work as a team. Let me describe the typical layout. The reservoir holds about one gallon of fluid, and it's located in one of the underfloor bays. It has a sight gauge that's visible so you can check the fluid level for replenishment — you can see when you need to top it up. The fluid is routed from the pump to four spray nozzles. And here's the key control feature: there are manually operated flow distribution and control valves located on the flight deck. These give you selective flow to the windshields — you can choose which screen gets fluid and how much. A single washer control button controls the fluid for both screens, as you can see in Figure 12.15. Now, the rain repellent system. This is a chemical approach. The system consists of four valve/timer nozzles — two for each screen — and a manifold. The manifold stores and distributes the fluid to the nozzles. It's charged with repellent fluid from an aerosol-type disposable container that screws into the manifold. So when the container is empty, you unscrew it and screw in a fresh one. The system has two important indicators. First, a sight gauge displays a refill float when the fluid is low — you see the float appear, and you know it's time to refill. Second, a pressure gauge has green and red areas to indicate a go/no-go condition. Green means the system is pressurised and ready to go; red means it's not. Here's the critical interpretation: if the float is visible, or if the pressure gauge indication is in the red area, then the container fluid is depleted. Either one of those tells you the container is empty and needs replacing. So to summarise the whole windscreen protection picture: you have electrical heating built in or as an optional panel, wipers that are two-speed and independently controlled for each pilot, washers that spray fluid through four nozzles with selective flight-deck control, and a rain repellent system with its own manifold, aerosol container, and go/no-go pressure indication. Each system has its own job, and together they keep the windscreen clear in ice and rain conditions.