From: email@example.com (Ed Hahn) Organization: The MITRE Corporation, McLean, Va. Date: 02 Feb 94 01:35:11 PST References: 1 Followups: 1
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In article <airliners.1994.893@ohare.Chicago.COM> firstname.lastname@example.org (Jay Vassos-Libove) writes: <stuff deleted> (Technical question, to justify the posting... WHY did Airbus design a 4 engine plane in the days of large Twins??) -------- This is because, to the manufacters and airlines, certifying a twin for Extended Range (ER) operations is a major hassle: -- The aircraft must demonstrate a certain number of flight hours without engine trouble before being considered for ER certification. This is to prove both that the engine can take it AND that a single engine (plus APU) would be sufficient to power the electrical, pneumatic (packs), and hydraulic systems to DIVERT to an emrgency field. A four engined aircraft doesn't even have to divert to a field and can continue on 3 engines to its original destination (in theory - in practice, most captains would elect to land ASAP). -- The individual airline must apply for ER certification to prove its maintenance program is up to snuff. -- Even with ER certification, according to FAA standards, you still have to fly at all times no further than a specified number of minutes from an emergency field (90, 120, or 180 minutes depending on the carrier/aircraft). If you want to operate in REAL remote areas (i.e. the pacific, etc), you are out of luck. The A340 has 4 CFM56 engines (same basic type certified for B737 and B757). Thus (obviously) ER certification does not apply, and because these engines are pretty good, fuel economy-wise, they aren't sacrificing that much. Conversely, the A330, which has the EXACT same fuselage and wing (except for engine pylons) as the A340, because it is a twin: -- requires new engines (i.e. GE90, PW4080, and RR Trent) and the attendent engine certification, -- ER certification, which the flying prototype has been demonstrating flying from Paris to Singapore or some other huge stage length (aside: would YOU want to fly for 20 hours a pop?) -- New engine maintenance programs on the part of the airlines. One example: the RR Trent cannot be transported as an intact unit on the back of a tractor trailer; the fan must be removed and broken into a several components, which then must be reassembled before installation. This is because the fan diameter is too wide and/or high for the US interstates (without Wide Load trailers). Anyways, the difference in range/payload between the A330/A340 is small enough that some carriers are willing to eat the operating differences. BTW, the B777 will be delivered to United with an ER certificate, but will be the first aircraft to be so certified at initial delivery... Hope this helps, Ed Hahn -- //////// Ed Hahn | email@example.com | (703) 883-5988 \\\\\\\\ The above comment reflects the opinions of the author, and does not constitute endorsement or implied warranty by the MITRE Corporation. Really.