Please elucidate with regard to “hard limit authority.”

I am referring to primary flight controls. For example, pitch. An Airbus will not exceed 30 degrees nose up in normal law no matter how hard you pull on the stick. If you pop out of a cloud and see a mountain and need to pull up momentarily to 35 degrees, you’re going to hit the mountain if you are in an Airbus, at least one of the modern ones (since A320). Likewise there are other hard limits.

With regard to Arthur’s comment about not getting into trouble in the first place, I agree. “A superior pilot uses his superior judgement to avoid situations which would would require use of his superior skill.” But sometimes, unforeseen scenarios occur. In those cases, it might be preferable to have human intervention be able to override the computer. The first priority for the passengers is keeping them alive.

Boeing hasn’t put hard limits into their flight control system because they believe the pilot should be the final authority over the flight controls, not some computer or computers.

There may be a situation where over-stressing the airplane is preferable to impacting the ground.

The Boeing fly-by-wire systems give progressive feedback as the airplane approaches structural or performance limits, ie., the controls get harder to move, but they can still be moved and those limits can be exceeded if the pilot in command feels it necessary to do so.

Given the alacrity with which some post their expert opinions (sic) on this message board (and criticize those who do not agree with them), I’m surprised there is not more awareness of this basic difference in flight control philosophy. The topic has been discussed ad nauseum in the Engineering and Pilot communities for over 25 years, since Airbus first introduced the hard limits on the A320.

Most cable driven flight control systems on large airliners (at least that I am familiar with) had feel mechanisms. This was one of the criticisms leveled by professional pilots against the A320 FBW system….lack of feel and no tactile feedback to the other pilot.

Granted, the B-29/Stratocruiser had a lot of electrical systems. However, comparing a 1940’s aluminum pistonliner with no electronics to a 2000’s era computer driven turbofan is quite a stretch.

The Strat tipped the scales at 148,000 lbs versus 502,000 for the lightweight 787.

The straight wing Strat cruised at just over 300 mph on a good day and could reach 32,000 feet if lightly loaded, the swept wing 787 routinely will cruise over 500 mph at the high to mid 30s. The strat spent most of its time in the 20’s and 200’s.

The Strat was pre computer, there were a lot of electrical systems by no electronics. The 787 has full authority (no artificial hard limits ala Airbus) fly by wire flight controls and many computers.

The pressurization for the Strat came from engine turbochargers, the 787 comes from electric fans.

The 787 has 4 250 KVA electrical generators, I’m not sure of the rating on the Strat/B-29, but I’m betting its less than 10% of that on the 787. This alone should give some indication of the degree to which the relative airplanes are dependent on electronics. Would love to hear what the gens on the Strat were rated at if anyone knows.

The 787 is over 50% composite, the Strat is mostly aluminum. Even this has been criticised with regard to electrical conduction during a lightning strike.

Comparing the Strat to the 787 is akin to comparing a Model T to a Lexus. Lose all electrical power on a Strat, fly all day long. Lose all electrical power on a 787, crash and die.

found the pic of the Eastern PNS aircraft. This is the way a DC-9 “normally” breaks after a hard landing:

http://www.airliners.net/photo/Eastern-Air-Lines/McDonnell-Douglas-DC-9-31/0077849/L/

Thats interesting because thats not where a nine usually breaks. Delta broke one in Tennessee in the 70’s, and Eastern broke one in Pensacola in the 1980’s, and they usually break just behind the wing and just in front of the engines. I don’t have the links handy but there are some grainy old pics associated with both of those incidents. I think Delta actually broke another one in half somewhere else also.

The nine normally lands a little firm because of the flight control system (“flying the tabs.”) An extra “anti-float” tab was added on the MD-80 series to help with that problem.

If I had to guess I would say an engine fitting/pylon/support frame was fatigued or damaged during an engine change.

Agree Arthur. I have no doubt that Southwest is driving the bus on the stupid cockpit to supposedly save pilot re-training costs. Darn them! How can one customer ruin a design for the whole industry?

I believe all of the approvals are for the Trent powered 787….the GE started flight test later and had only 2 airplanes….it was always planned to certify the Rolls and then the GE.

787 Certificated

FYI, I posted this on the other thread, but its kind of buried….not sure if everyone is seeing it.

http://boeingblogs.com/randy/archives/2011/08/the_dream_is_certified.html