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Old 03-28-2011, 02:11 PM   #1
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1 engine vs 2 (airplanes)

I noticed this today and could not let it go by without a comment since it represents such a universal misconception.* I sent a PM to Phil but thought I'd go ahead and stick it here too.* It's very long* because it's not an issue that can be reduced to stupid, simplistic comments like "Airbus planes are made for bad pilots."* If anyone wants to discuss this further please PM me-- I won't discuss it here.

Phil asked--- "Just curious - do 767's have more flight diversions than 747's, on long haul flights? Or DC-10's? Perhaps the 777 have newer engine technology, so more reliable.....And - as an aside - what's your thoughts on Aerobus and fly by wire?"

Phil---

Airliner diversions and in-flight engine shutdowns have nothing to do with how many engines are on a plane.* They are almost always the result of a system problem, not an engine problem.* By system I mean hydraulic, electrical, pneumatic, etc.* I was on a flight that had to turn back because one of the cooling fans in the instrument panel conked out right after takeoff.* Cooling the panel displays was a go/no-go item on this particular plane. I've experienced a four-hour flight delay because one of the windshield wiper motors on the plane failed and it's an FAA requirement that the wipers on a plane must be operable if it's raining within ten miles of the airport [I may be misremembering the distance--- it might be five miles or more than 10].* If the wipers are not operable, the plane cannot depart.* It took four hours to locate and install a new motor.* In fact the airline (Continental) finally had to send someone over the final assembly line in Renton to take one off a plane on the line.)* I know pilots of planes that had to do an emergency diversion to an alternate airport because the toilet system on their plane failed.* Engines are right down at the bottom of the list in terms of diversions or in-flight emergencies.

The variety of turbofan engines used on today's planes is very small.* The 767 uses the same engines as the 747-400.* The 747-8 uses the same basic engine as the 787.* The 737 and the A320 use the same basic engine.* The basic GE engine used on the 777 is also used on several Airbus models.* Almost all GE engines today are derived from the same basic core, as are almost all Rolls Royce engines.

There is only one "rule" with regards to the number of engines on an airliner.* And that is that any commercial jetliner must be able to lose one engine at the most critical point in a takeoff and be able to continue the takeoff and climb out albeit at a reduced rate of climb on the remaining engine or engines.* A twin-engine jetliner that loses both engines is in a world of hurt, but so is a three or four engine jetliner that loses more than one engine.* Three or four-engine planes don't have that many engines for safety, they have that many engines so they can fly.* This is why twin-engine planes are so overpowered--- they have to be able to continue the takeoff and fly if they lose one engine.* A 747 has to be able to continue a takeoff on three engines if it looses one, but it doesn't have to be able to continue a takeoff (and it can't if it's fully loaded) if it loses two.

With regards to fly-by-wire and the differences beteween Airbus and Boeing, these are the most misunderstood things in aviation and few people outside the industry actually understand them.* With the exception of Johh Baker, nobody on TrawlerForum understands them based on what I've read in their posts.

Fly-by-wire is simply the means of getting control inputs from the flight crew or the autopilot to the flight control actuators on the wings and empennage--- ailerons, flaps, spoilers, rudder, elevators, etc.* It has NOTHING to do with the flight control philosophy that's programmed into the plane's flight control computer system.* The A320, A330, A340, A380, Boeing 777, and Boeing 787 are all fly-by-wire airplanes and we both use components from the same suppliers.* Fly-by-wire is simply a physical flight control system.* Fly-by-cable uses cables to transmit commands to the actuators, fly-by-wire uses electrical signals down wires, and fly-by-light uses light pulses transmitted down fiber-optic cables.

The difference between Boeing and Airbus is in our flight control philosophies, which have nothing to do with how the control commands are transmitted to the actuators.

Airbus' flight control philosophy is to prevent the plane from being flown in a manner than would exceed the aerodynamic or structural limitations of the airplane.* There is nothing wrong with this, and the notion that Airbus' planes are designed for bad pilots is total bullsh*t and is what people who haven't a clue what they're talking about will say.* There are very real benefits to the Airbus flight control philosophy--- I know of one fatal crash of a Boeing plane that had the plane been an Airbus it is very likely the crash would not have occurred.* The Airbus philosophy of preventing a machine from being operated in a manner that exceeds its safety parameters is very European, and you will find the same philosophy applied to European trains, ships, cars (to a degree), and industrial applications like power and water plants and whatnot.

Boeing's flight control philosophy is also culturally-rooted, but in this case it's the US culture.* Our (I work for Boeing) philosophy is that we will allow the flight crew to exceed the plane's aerodynamic and structural limitations to the point of destroying the plane, BUT..... we will make it totally obvious that they are doing so.* So the control inputs--- column, yoke, and rudder pedals--- get very difficult to move and all sorts of audible and visual alarms go off on the flight deck.

An example of the benefit of Airbus' philosophy is if an airplane is slowed to point where the wing could stall, the leading edge devices will automatically be deployed to allow the wing to fly slower without stalling even if the flight crew forgets to deploy the leading edge devices themselves.* In the case of the fatal crash of a Boeing plane I mentioned earlier, the plane was pulled up to avoid an obstacle which slowed the plane to the point of stalling.* In the panic of the moment, the flight crew did not extend the leading edge devices, the plane stalled, and crashed.* Had the plane been an Airbus the leading edge devices would have deployed automatically as soon as the plane approached stall speed even if the flight crew was too distracted to do so and the general consensus is that the plane would not have stalled and instead would have cleared the obstacle and flown away.* There is no way to know how many accidents or incidents are prevented by Airbus' philosophy because if an accident or incident doesn't happen we either don't realize it was about to, or we don't really know for sure after the fact why nothing bad happened.

An example of the benefit of Boeing's philosophy is if an airplane is on very short final and is slowed down for touchdown and is hit by a sudden and violent microburst.* It the flight crew adds full power and hauls way back on the yoke in an attempt to keep the plane from striking the ground there is a 99.999 percent chance the plane will stall and crash.* BUT.....* air being the unpredictable thing that it is, there is a tiny chance that if the flight crew adds power and hauls way back on the yoke the plane MIGHT not stall and MIGHT not strike the ground.* And missing the ground by a tenth of an inch as as good as missing it by a mile in this instance, so the plane MIGHT stagger off down the runway in ground effect until it builds up enough speed to be flown away safely.* So Boeing gives the flight crew the opportunity to do this even though it probably won't work 99 percent of the time.* An Airbus, however, would recognize the power setting and airplane pitch input and speed as being well outside the aerodynamic and possibly the structural limitations of the plane and so would not allow the plane to be pitched up so high at that speed in that configuration.

That is the difference between the Airbus and Boeing flight conrol philosophies.* It has NOTHING to do with fly-by-wire.* These same philosophies can be applied to fly-by-cable or fly-by-light.* Fly-by-wire makes it easier to program these philosophies into the flight control computer system which is why the Airbus philosophy is always being connected to fly-by-wire.* But in reality their philosophy has nothing to do with fly-by-wire. As I said, Boeing's newest planes are fly-by-wire too.

So it's like the twin engine boat vs. single engine boat issue.* Which is better?* Depends on the boater's priorities and situation.* Neither one is inherently better than the other..* Their "betterness" is tied to each individual application.* In the case of the Boeing crash I described earlier, the Airbus philosophy is clearly superior.* In he case of the microburst scenario the Boeing philosophy at least gives the flight crew a chance of saving the plane.

Since I work for Boeing, I'll give you one more pro-Boeing scenario.* I produced a number of videos supporting our bid in the recent USAF tanker competition.* One of the* most effective (with the USAF) demonstrated the capabilities of the 767 in the event it was a target of a SAM launch in a combat zone.* We filmed the scenario in the full-flight 767 simulator which mirrors the actual airplane's capabilities and attributes in every way.* When the flight crew-- which for this exercise was a military flight crew--- detected the SAM launch and missile approach they took the prescribed evasive action which is to disconnect the autopilot (a button push), whip the plane over in a roll of about 110 degrees (so slightly upside down), pull the power off, and dive almost vertically for the ground.* When the crew did this all sorts of alarms went off on the flight deck to warn the crew they were exceeding a whole bunch of* limitations, but the plane responded exactly as commanded and the missile was evaded.

This maneuver would have been impossible to fly in the EADS Airbus A330 tanker because the A330s flight control computers would not have allowed the plane to be rolled this fast or this far or pitched over into this steep of a dive.* And there are a bunch of reasons why their flight control computers cannot simply be re-programed to respond like the 767 did, some of which have to do with their selection of a joystick rather than a control column and yoke as their primary control input device, and the nature of that joysitck.

To be fair, an Airbus can be set up to give the flight crew the ability to exceed all the plane's aerodynamic and structural limitations just as they can in a Boeing.* BUT..... it takes a bit of time to pull the necessary breakers and punch through the various setup commands on the flight control computer input device.* In the case of the SAM launch, the missile is not going to enter a holding pattern and patiently orbit while the Airbus crew sets up their plane to be able to take the violent evasive action necessary.* Also, because of the nature of Airbus' joystick, disabling the flight control limitations increases the likelihood of the flight crew tearing the wings off the plane in the course of executing the evasion maneuver in which case it wouldn't matter if the SAM hit it or not.

So.... two different flight control philosophies, both of which have their advantages and disadvantages, and neither one of which have squat-all to do with fly-by-wire.

Sorry for the long commentary but perhaps you can now understand why this whole issue is far more complicated that the stupid, simplistic statement that "fly-by-wire is for bad pilots," or that Airbus is bad and Boeing is good or visa versa.


-- Edited by Marin on Tuesday 29th of March 2011 02:36:59 AM
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Old 03-28-2011, 02:58 PM   #2
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RE: 1 engine vs 2 (airplanes)

Marin... excellent article... and welcome back (we hope).

Having been an author of tech pubs for both Boeing and Airbus, I've seen some of the range of both firms.

I always viewed the 1 engine or 2 scenario on aircraft as simple:* I'd rather have 1 engine fail on a 2-engine aircraft, than have the only engine fail on a 1-engine

Of course, I realize that's not what you were discussing, but I had to get it in.
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Old 03-28-2011, 03:05 PM   #3
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RE: 1 engine vs 2 (airplanes)

Welcome back Marin. You certainly are in good form. I learned a lot too.

But, KMA, it depends on when one engine on a twin fails. I sat next to a couple in ground school years ago...a doctor and his wife...that owned an Apache. One cold morning the couple, two kids and his nurse and daughter started off for Vegas. One engine quit on take off. the dead engine went down and they cartwheeled the plane. No survivors.
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Old 03-28-2011, 11:15 PM   #4
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RE: 1 engine vs 2 (airplanes)

Quote:
Doc wrote:
...a doctor and his wife...that owned an Apache.........* No survivors.
******* in 1967 I got my multi engine rating in a Piper Apache. Single engine rate of climb was terrible and my instructor said that the difference between the Apache and a single engine plane was that in an engine out situation in the Apache you get to pick your crash site.
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Old 03-28-2011, 11:37 PM   #5
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RE: 1 engine vs 2 (airplanes)

Quote:
DavidM wrote:
This focusses his attention and it often ends reasonably well. I agree.

*First and most critically the pilot must apply extensive rudder force to ovecome the assymetric thrust. Except for planes like the Twin Comanche CR. (Counter Rotating)
*

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Old 03-29-2011, 04:40 AM   #6
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1 engine vs 2 (airplanes)

"And that is that any commercial jetliner must be able to lose one engine at the most critical point in a takeoff and be able to continue the takeoff and climb out albeit at a reduced rate of climb on the remaining engine or engines."

And that ability makes the aircraft with both engines working have performance that would amaze /delight a WWII pilot!

"Airbus' flight control philosophy is to prevent the plane from being flown in a manner than would exceed the aerodynamic or structural limitations of the airplane. There is nothing wrong with this, "

I think the two sets of Air Bust "Test Pilots" that crashed at the Paris Air show, two different years, might have a different opinion of the joy of a flight philosophie that caused them to demonstrate a crash and burn.

Interesting video , yet Air Bust persists, and sends "Jocks" to show off their products.


-- Edited by FF on Tuesday 29th of March 2011 04:42:00 AM
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Old 03-29-2011, 05:07 AM   #7
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RE: 1 engine vs 2 (airplanes)

Yes, welcome back Marin, we missed you. Good explanation there. Would you care to comment on the Air France and the pitot tube issue, and the part the Airbus computer control might have played if it was being sent conflicting information re air speed/altitude etc, and how that might differ from the same scenario in a Boeing? I see they are launching yet another attempt to recover the wreck.
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Old 03-29-2011, 01:23 PM   #8
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RE: 1 engine vs 2 (airplanes)

Peter, you beat me too it..
I watched the "docu-drama" on PBS I think it was, on this horrible AF crash.

according to this tv program, the possible faulty pitot tube meant the crew got a faulty airspeed reading (disabled all the a/p and electronic flight systems which the airbus relies so heavily upon) eventually leading to a high altitude stall.
the crew could have prevented by setting a "known thrust setting" (they had reduced thrust initially when the a/p failed and never re-applied thrust) and brought the plane into a slightly pitch up (actual degrees in the manual). This configuration would have placed the a/c in a safe speed.
at the end of the show, there was a short discussion about just this..
this generation pilots fly planes like computers, turning dials and setting codes. when an actual situation like this occur they may not have the depth and training to be dealing with all the faulty systems AND their PRIMARY responsibility.. to fly the plane.

btw, i was multi trained in a piper seneca II at a high altitude new mexico airport, talk about density altitude. flying one engine with the bad one fully feathered produced a controlled descent at best.

loosing an engine on take off in a light twin is the biggest challenge most pilots would probably ever face, if they survive..
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Old 03-30-2011, 04:43 AM   #9
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RE: 1 engine vs 2 (airplanes)

"they may not have the depth and training to be dealing with all the faulty systems AND their PRIMARY responsibility.. to fly the plane."

Switch position "pilots" are taught to NOT fly , as the information on winds aloft , best rate of climb at current CG and OAT ,is best handled by the AP.

Fuel burn is King !

The lack of flying skills may only mean an extra training ride in the Box (every 6 months) , just electric , no fuel use.
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Old 03-30-2011, 12:09 PM   #10
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RE: 1 engine vs 2 (airplanes)

Quote:
FF wrote:
"they may not have the depth and training to be dealing with all the faulty systems AND their PRIMARY responsibility.. to fly the plane."

Switch position "pilots" are taught to NOT fly , as the information on winds aloft , best rate of climb at current CG and OAT ,is best handled by the AP.

Fuel burn is King !

The lack of flying skills may only mean an extra training ride in the Box (every 6 months) , just electric , no fuel use.

*

*except when the pitot tube freeze over and cause all the a/p and all automated systems to shut down, time to fly by hand (still flybywire though).

*
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