Yous all better watch out. I bild airplains at Boeings. I makes shur all the wirin and lectricul stuff works okay. I can probly fly an Boeings airplain with all the trainin and stuff we have to do.
Some other testing tidbits from Boeing. One of the first 777’s that came down the assembly line was built to be a pressurization test mule. For over 3 years that fuselage was pressurized and depressurized (one cycle) ever 17 minutes around the clock. At the end of the test the fuselage would still hold pressure at 107% of the minimum required by the FAA.
The first 737 Next Generation aircraft went through over 400 test flights. Only 2 were delayed by part failures.
The forces operating on a “mere” 2 ton airplane are greater than those on a 2 ton car as well. Which is why the lowest standard for aircraft certification requires the airplane to be able to withstand over 2 g’s of force, where cars do not have this requirement. Also, cars are not required to impact pavement on a regular basis - even a gentle landing exerts considerable downward force on the landing gear. Cars are not expected to keep working when it’s 40 below zero, but airplanes are (it gets cold up there!). Cars do not have to be able to compensate for the air pressure dropping by 1/3 or 1/2 but airplanes do (even unpressurized ones). When you drive your car, you do not start your journey by flooring the gas pedal for 20 minutes, then running at 75% of maximum power thereafter, but that’s considered normal for airplanes.
I’m going to quibble with this slightly. Aircraft weight is shaved where the weight can be spared, but at times strength is required. One of the airplanes I fly is an aerobat, which is rated for up to 6 g’s. At 6 g’s the airplane itself weighs 6,600 lbs, not including the weight of fuel and passengers (fuel @ 6 g’s = 36lbs/gal, me at 6 g’s would be around 900 lbs, which is just one of the reasons I don’t want to try this). That’s a lot of weight supported by an 1100 lb structure, and not even all of that structure is doing the supporting. The weight is shaved only where strength is not essential, such as cosmetic detailing. Which is also how they shaved the weight and improved the gas mileage on my Echo, by building the cosmetic stuff out of lighter materials. The dash in the Echo, for instance, is made out of a very lightweight plastic because the shape of the dash is mostly cosmetic and does not contribute to the overall strength of the car.
As another illustation of how airplanes can be surprisingly tough, a couple years ago in Florida two airplanes approaching an airport to land had a slow-speed collision and they locked together, one airplane on top of the other. Specifically, it was a Piper Warrior (about 2300 lbs with instructor and student) on top of a Cessna 150 (about 1300 with the pilot). Well, they did land, with the bigger airplane on top of the smaller, and the small airplane was able to support the weight of the bigger airplane at touchdown and along the runway. They got a crane of some sort to hoist the big airplane off the little airplane, but apparently both machines only suffered minor damage. Somehow, I don’t think the average car would function as well with a bigger car on top of it.
Why the difference? It’s the way they’re built, not what they’re made out of, that makes a difference. But then, a new airplane easily costs 10 times what a new car does.
On the other hand, a pocket knife can go through the skin of a small plane, but I’d have a much harder time doing that with a car’s exterior (scratch it, yes, cut it, I doubt it). If a car hits an obstruction on the ground at, say 10 mph you might get fender damage and set off the airbag, but if a small airplane runs into a runway light at the same speed you might be looking at major damage (a busted prop, a busted wingspar, maybe a ruptured fuel tank in a low-wing). It’s because the odds of an airplane hitting an object when operated properly are much lower than those of a car doing so. Both vehicles are designed to withstand the forces they normally encounter. Airplanes have to be able to slam into pavement, cars don’t. On the other hand, cars are more likely to hit things on the ground, so we design them to be able to withstand those impacts more than airplanes can.
Another quibble.
First of all, very few people start their training in larger airplanes. Many small airplanes are training airplanes, meaning they are flown by people who aren’t fully trained. They take a hell of a beating from bad landings alone. Bigger airplanes, being much more expensive (and more dangerous during a screw-up) are almost always flown by the more experienced and better trained pilots. So who’s sitting at the controls has a definite effect. This is why a privately owned C712 only needs an annual inspection but a trainer airplane owned by a flight school needs an inspection every 100 hours of operation - and usually some minor repairs on top of that. Think of the difference between a driver’s ed car and a car owned by an adult with 20 years driving experience. Which one is more likely to have problems? It’s not the design, it’s the (ab)use it gets.
Agreed that the pilot does have an effect on safety, and to a large extent a bigger, faster airplane is less affected by weather, which is why I’ll fly a 4-seat Warrior in higher winds than a 2-seat Cessna. But the limits of an airplane is published in the manual, and I don’t think the small airplanes suffer a disproportionate number of weather-related accidents. And if a Cessna Skyhawk goes down in a thunderstorm it’s not a design fault - it’s the fault of the idiot who got himself into that situation in the first place.
Beyond a certain point, however, avionics do not appreciably affect flight safety. There is some redundancy built into even the smallest factory-built airplane. Two radios, for instance, is pretty standard, but even without radios a small plane can make a safe flight. In fact, once upon a time I flew an airplane without a working electrical system 70 miles to get it to the repair station. No radio, no engine gauges, no fuel gauges, no navigational equipment, no transponder, only one of the two fuel pumps working, no lights… the only dials working were the airspeed, altimeter, and the artificial horizon. And I didn’t bother with the latter because I didn’t need it, the weather was so nice. Perfectly safe and legal flight, although I wouldn’t have launched such an airplane in questionable weather, or with night coming on. Part of my training involved learning to fly the airplane despite instrumentation failures - and, as a “mere” private pilot I’m not nearly as well trained as the guys in the 747. But there’s a difference between having something go wrong in flight, and taking off with something already wrong. Like the time I returned an airplane early because the altimeter quit working. The guy at the front desk gave me a hard time - “You’re a good enough pilot you don’t need an altimeter”. Well, yes, that’s true, I can fly without one, but that skill is to get me home in the event the altimeter quits, it’s not to allow me to take a defective airplane into the sky.
And my final point - although you ARE more likely to have an accident in a smaller airplane, you are also more likely to survive it. When a jumbo jet slams into something on a take-off run, it hits at over 100 mph. When I hit something on a take-off run (so far, this hasn’t happened) I hit it at 50 or 60 mph. That’s still really bad, but more survivable. Likewise, on landing, the big guys are still doing 100+. Me, I’m as low as 45 mph. That’s more like a bad traffic accident than what’s typically pictured as a plane crash. Still wouldn’t want to have it happen to me, but the forces involved are much smaller and more survivable.
A commercial airliner is much much more durable than an automobile. Design life for most B**ing jets is about 60,000 hours. A car’s life, assuming 150,000 miles at 30 miles/hour, is maybe 5000 hours.
Commercial airliners have “A” checks, which are generally minor visual inspections, analogous to checking the oil level in you car, “C” checks, which are checks of proper systems operation, and “D” checks, which are generally heavy-duty structural inspections. “A” checks are at about 300 hour intervals, “C” checks at about 3000 hours, and I don’t offhand remember what the "D"check interval is.
That would depend on the car. In the 60’s Volvo stacked 6 140 series Volvos one on top on the other. No damage. (Although I did see a video of them doing this in Sweden and a gust of wind caused a guy wire to break and it was raining 140s all over the lot.) In the latest copy of Motor Trend there is a sidebar to the intro story on the XC90 SUV that talks about a rollover test, and it mentions that the impact of the unit at 30mph rolling over is 78,000 lbs spread over just a few square inches. The pictures show that the roof survives. With damage to be sure, but intact enough that any passengers would survive.
Nits are now all picked and we return to your regularly scheduled aircraft maintenance thread.
On that subject are there some airlines that you won’t fly because you feel the maintenance is not up to par?
