"Poor aerdynamics ???Those whole play no part in that." Sorry, guys.... I realize now that some of you don't understand my wierd sense of humour... It was supposed to be a joke... even though some of you might be aware that aircraft designers were experimenting with boundary layer modification using very small holes on the upper wing (I even believe these holes were hooked up to the bleed air system in some cases). That is not to say that the minor turbulence created by the hot anti-ice air coming out of the holes won't affect the airflow in some minor/incosequential way.For the sake of clarity, I will now refrain from all joking :-lol (That, by the way, was another of my weird jokes ;-))Cheers.Ian.

"15 min. later he told us, that one of the hydraulic systems was failing and that we shouldn't worry, because the 747 has three hydraulic systems as backup. Is that true?"Correct... but not all flight controls can be powered by these back-up hydraulic systems. The Inboard TE flaps are driven only by one hydraulic system and the Outboard flaps are also driven by another single hydraulic system only (On the 747-400, at least, the flaps will automatically switch to ("primary") electric mode if the hydraulics fail to retract the flaps). Failing that, there is manual electric control. The electric systems are much slower than the hydraulic system.On the 737NG, the trailing edge flaps are (normally) mechanically controlled and hydraulically powered. The Flap Lever is connected to mechanical cables/pulleys which operate a valve which operates a hydraulic drive motor which drives the flaps in/out. Hydraulic System "B" is used. Hydraulic system B can be powered by the R/H engine hydraulic pump or by the B system Electric Hydraulic Pump (switch on overhead panel). If both of these hydraulic pumps fail, there are two back-up pumps for hydraulic system B. However, neither of these are able to drive the Trailing Edge flaps (only the Leading Edge Flaps... but these will only operate under certain circumstances/airplane configurations).There is an electrically operated, electrically powered back-up system. Selecting ALTERNATE FLAPS on the overhead panel and toggling the UP/DOWN switch (next to it) extends/retracts the Trailing Edge Flaps. CAUTION: You can stop the TE flaps extending by releasing the DOWN switch (it is spring loaded), but the LE flaps/slats will continue to extend. The only way to stop the LE slats/flaps extending is to switch the ALTERNATE switch to OFF.Hope this helps.Cheers.Ian.

>CAUTION: You can>stop the TE flaps extending by releasing the DOWN switch (it>is spring loaded), but the LE flaps/slats will continue to>extend. The only way to stop the LE slats/flaps extending is>to switch the ALTERNATE switch to OFF.Oh! Good to know. Because after the detailed explanations provided by you and Paul I feel like able to get a real 737 and fly it. :-lol No, all the real pilots out there, don't worry. I'm not gonna do it.:-) And Ian, please don't stop with your weird yokes!Thanks to both of you.RegardsThomas

My dear Ian,I have eventually reached the age where heart attacks are likely. Given that your opinion is considerably valued in these quarters please please mind your titles in the posts so that this poor flight dynamics developer does not suffer one :-) Where the heck are those pills now ?Best Regards,VangelisPS. The wing of the NG is a work of art. The wing itself can do more than Mach 0.84. It is the massive tail structure that limits MMo to 0.82...For something that can take off and land at little over turboprop speeds (check the -600 data) and allows fantastic performance from low subsonic to high transonic speeds this is an extrordinary accomplishment.===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

"please please mind your titles in the posts so that this poor flight dynamics developer does not suffer one Where the heck are those pills now ?"LOL... Point taken, Vangelis ;-) I was going to write a message titled "PMG Output Bad" a few days ago when the Permanent Magnet Generator on one of our Integrated Drive Generators failed to produce enough volts, but then I thought the acronym was a little too close for comfort :-hah"For something that can take off and land at little over turboprop speeds (check the -600 data) and allows fantastic performance from low subsonic to high transonic speeds this is an extrordinary accomplishment."Sounds like a line straight out of the glossy Boeing sales brochure :-lol Where can I buy one?Anyway, no more vortex generating from me for a few hours... Time for bed. To sleep, perchance to dream... of 737NG's :-)Cheers.Ian.