In Part 1 (featured at NYCAviation.com), I talked about what happens when stuff on an airliner breaks while we sit at the gate. What do airline pilots do when there is a mechanical malfunction while airborne? Airliners are really complex machines. Just like in your car, sometimes stuff stops working the way it should. Read on to see what we do and how redundant systems keep you safe even when stuff stops working in flight.
The vast majority of flights take place with absolutely nothing going wrong. Modern jet transports are marvelously reliable (even the 30+ year old airplanes). Occasionally, we run into a problem.
Irritating Problems <shrug>
Remember the broken tachometer in your 1977 Ford Pinto? The tachometer is nice to have, but it isn’t a big deal if it doesn’t work. You can drive around safely all day without one.
A similar example in an airplane would be a faulty clock. My aircraft has two of them but we don’t need any to fly safely. If it stops working, we write it in the logbook then resume our discussion of last night’s World Cup match. For the remainder of the flight we’ll use an iPhone as our oven timer.
Small, irritating problems like this happen in airplanes about as often as they happen in your car. A light bulb will burn out or a radio tuning knob will get loose. No big deal.
Check List Problems: Most are not a big deal
As you might guess, we have systems on the aircraft that are a little more important than the clock. For the really important stuff, we have a “Non-Normal Checklist.” When we see a warning light or message on our alert screen, there is a procedure we must follow. The Non-Normal Checklist gives us step-by-step guidance on how to correct or secure the malfunctioning system.
Uh-oh. R HYD PRIM PUMP We just received a warning that our Right Hydraulic Primary Pump has failed. Our hydraulic system powers all the flight controls on the aircraft. Sounds serious, doesn’t it? Surprisingly, the checklist only has two steps:
1. Primary Pump Switch: OFF
2. Continue Normal Flight
That’s it? Yep. My 767 has three separate hydraulic systems. Any single system can bring the jet home safely. There are a total of seven independent hydraulic pumps supplying pressure to the three systems. An eighth pump is powered by a ram air turbine (a windmill) in case we have a really, really bad day. The pumps rarely fail, but if one does, we have plenty of other pumps. After we finish running the short checklist, we put the problem in the logbook. Maintenance will fix the pump at our next destination. Again, we are back to discussing the World Cup until it’s time to descend.
Check List Problems: A few are a BIG deal
Although airliners have plenty of redundancy, there are rare occasions when a problem makes it necessary for the crew to land at an airport other than your destination. This is called a diversion.
My aircraft has three generators to power its electrical system. The chances of any generator failing are very small. But if, by some bad luck, two of our generators stop working, the Non-Normal Checklist will recommend that we find a nearby airport and land as soon as possible. When there is no longer redundancy of a major system (like hydraulics, electrical, or engines), it’s time divert. The cargo customers and/or passengers will, unfortunately, be inconvenienced for safety.
If We Need To Divert To Another Airport…
In this situation, cockpit discussions concerning the World Cup are immediately suspended. There is a lot of work to be done. We need to find an airport that has a runway long enough to accommodate us and good weather to assure a safe landing. Finding a nearby airport that is serviced by our airline is a bonus but not a prerequisite. It’s always nice to get extra help. If time permits, we will contact our dispatcher by radio or satellite phone. Dispatchers can quickly sort through the weather and available facilities at nearby airports and make recommendations. Air traffic controllers will give us preferred routing and keep other aircraft out of our way so we won’t be delayed. While landing, you might see a few firetrucks along side the runway. This is most often just a precaution. It gives the fire and rescue crews some practice and it’s nice to have them standing by in case we need them. Once we are on the ground, maintenance personnel will begin to work on the problem. More importantly, the airline will try to find the fastest way to get a planeload of passengers or cargo to their final destination.
Diversions In The News
The majority of airliner diversions or cancellations are due to bad weather. Weather diversions happen routinely enough that they aren’t newsworthy. An airliner diverting due to a mechanical problem is very rare, so it usually makes the evening news. Don’t let the news reports fool you into thinking that airplanes are unsafe. In my 25+ year airline career, I’ve diverted only twice for mechanical problems. There are about 100,000 scheduled airline flights every day. If the news media reports an aircraft diversion once every 10 days, that represents one serious problem for every million flights. Even a frequent flier is unlikely to experience a mechanical diversion.
Have you been a passenger on a flight that had to divert due to a problem? I’d love to hear about it in the comments below!