“Does an aircraft have a horn?” “Do you need a key to open an aircraft door?” “Where do the aircraft names come from?” You might recognise some of these questions from the #JesseyKnows series. Or you might have wondered about some of these same things. Now I’m picking up the baton.
Hi there! My name’s Annelinde and I’ll be answering all your questions in #AskAnnie. So I’ll just jump right in. How do you change the wheels on an aircraft? You’ll find out soon enough.
When I think about the wheels on an aircraft, I imagine gigantic wheels, as big as a lorry. Think I’m exaggerating? OK, maybe a little. But I really did think that. Now I know better. But they are big. Let’s be clear about that. They’re about a metre-and-a-half tall – it differs from one aircraft to the next, and wheel position. They can weigh between 200 and 250 kilos. Not the sort of thing you’d like to have roll over your foot, I imagine.
The Boeing 777-300ER weighs 251.000 kilos and is held up by fourteen wheels. That works out to no less than 12,000 kilos per wheel. So you can imagine that there’s quite some pressure on the wheels when they’re taxiing, taking off, and landing. Can you even imagine how they get changed? Do you have to lift up the entire plane? I don’t imagine so. But I had to find out. So I was off to Schiphol to the Line Maintenance division at KLM Engineering and Maintenance.
On the airside
My day started at Schiphol Airport security. First to the airside, which includes the apron, where the aircraft stand. But first I have to make some preparations. I must be wearing safety shoes, a safety vest, and my badge. I walk around with a gentleman named Ferry. He’s from the Line Maintenance division, which checks all KLM aircraft on the airside after they’ve landed. First I accompany Ferry on his rounds over the apron. He tries to explain to me – a twit without a driving licence (and who can’t even patch her own flat bike tyre) – what everything does. And he manages pretty well. Listen to this.
It has to do with wear and tear
Changing the tyres has to do with wear and tear. The tyres have deep grooves that help remove water in the event of a wet runway. The grooves have a specific depth when they are new, but they wear down with each takeoff and landing. When the grooves are less than 0.2 millimetres thick, they have to be changed. Each time a KLM flight lands at any airport, a ground mechanic does a check of the aircraft and measures the tyre grooves.
Here’s a fun fact: Taxiing is tougher on the wheels than taking off and landing. As you can see in the photo, the grooves in the wheel to the left are almost gone compared to the one on the right.
As soon as a wheel has to be changed, a message goes to the warehouse. A runner comes with a special wheel truck, which the KLM technicians designed together with the truck manufacturer, and which loads the wheel. The wheel truck is designed so that the runner has everything he needs to change the tyre. No other airline has a wheel truck like this. The truck has two jacks, the tool trolley, a seat, and a “tyre lift.”
Nitrogen it is!
On the outside of the truck, you’ll find two places where wheels can be attached – and nitrogen. You don’t pump up aircraft tyres with just air. You use nitrogen. Nitrogen is an “inert” gas. That means it hardly has any chemical interactions with other substances. So the tyres remain at the right pressure for longer than when you use normal air. As a result, they wear down less quickly.
This is how you change them
I saw it during my visit. That day, it turned out there was a Boeing 777-200 with a wheel that was no longer up to standard. The aircraft had to depart for Lima, Peru within two hours. I was going to see it with my own eyes. The cabin attendants were ready up above and the passengers would board an hour later. Just enough time to change the tyre! How do you do that? I’ll take you through it, step-by-step.
For all clarity, Line Maintenance always work in twos to change the tyres. It goes like this:
- The runner arrives with the wheel truck. The pair of ground mechanics wait for him at the wheel.
- They place the jack under the lift point in the landing gear. After all, you can’t put the jack just anywhere. The jack is driven by pressurised nitrogen. Slowly, the landing gear rises.
- While it elevates, one of the mechanics goes to remove the hub cap. He protects the retaining nut which keeps the wheel in place.
- When the wheel is sufficiently elevated, he can remove the retaining nut. Important: The wheel rim consists of two parts and is held together by many nuts and bolts. But you mustn’t loosen those or the wheel will fall apart.
- A cable is loosened. Wait. A cable? Yes, but not just any cable. It tells the pilots if the tyre pressure is correct. The cable is attached to a sensor which is connected to a tyre valve, which sends information to the cockpit.
- They remove the tyre from the axis using the wheel lift. They’re very heavy. You can’t put them down and roll them around.
- And you can’t just slide the new one on. The brake has to come in contact with the wheel. This occurs with the help of recesses in the brake discs and conductors in the wheel rim.
- They re-attach the retaining nut and connect the cable to the valve. They tighten the small nuts and bolts around the retaining nut. This is an extra safety measure so that the large nut can’t loosen when the wheel turns.
- Last of all, the hub cap goes on and the mechanic checks the tyre pressure. If necessary, he’ll pump in a little more nitrogen.
Now the aircraft can depart for Lima with a brand-new wheel. Have a good trip!
Now, I can continue walking around to another aircraft like a real tough guy in my vest. It doesn’t need its tyres changed but, if it did, I’d know how.
If you have a question about aircraft, the aviation industry or KLM, don’t hesitate! Tweet or Facebook the question with #AskAnnie and who knows, I might look it up for you.