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Aviation Forum / Country Specific / Australian Group / February 2010Power settings on climb outs for B767s?
A report in today's paper talks about a tail scrape by a QF 767 as it left SYD for MEL. After the aircraft returned a 33 yo pax was "interviewed". She said: "Passenger Nicole Kearns, 33, who was flying with her one-year-old son, said she thought she detected the pilots throttling off to slow the engines while the plane was still climbing." More here. http://www.theage.com.au/travel/travel-news/qantas-plane-drama-after-tail-strike -20100202-na83.html Is the thrust reduction during the climbout normal? I seem to recall this happening, or had the perception of it occuring on flights that I've been on. > A report in today's paper talks about a tail scrape by a QF 767 as it left > SYD [quoted text clipped - 15 lines] > happening, or had the perception of it occuring on flights that I've been > on. Flight below 10000 is 250 kts. Takeoff thrust would take you in excess of 250 kts. Yep, I think there would be some reduction in thrust. >> A report in today's paper talks about a tail scrape by a QF 767 as it >> left SYD [quoted text clipped - 18 lines] > Flight below 10000 is 250 kts. Takeoff thrust would take you in excess of > 250 kts. Yep, I think there would be some reduction in thrust. Speed would depend on the pitch attitude. Anyway, what is "takeoff thrust" in a world of de-rates or flex thrust or reduced thrust takeoff? I think I recall that minimum takeoff thrust was not to be less than initial climb thrust. Cheers, > Flight below 10000 is 250 kts. Takeoff thrust would take you in excess of > 250 kts. Yep, I think there would be some reduction in thrust. Not necessarily. Full charge and about 20-25° would give you a stable speed below the limit. Level flight would, of course, be a very different matter. In any event, even on derated take-offs, there is normally a very large thrust reduction, back to a derated climb thrust, on the 767. Only aircraft that I've ever flown on which there may be an increase in thrust is the A380.  SignatureRead the latest aviation news at www.flight.org > Only aircraft that I've ever flown on which there may be an increase in > thrust is the A380. Seems strange. How does that arise? Sylvia. > > Only aircraft that I've ever flown on which there may be an increase in > > thrust is the A380. > > Seems strange. How does that arise? 'Cos the Boeings are limited to a max take-off derate equal to climb power, whereas the AB isn't. So, on a light weight take-off (440 tonnes), the AB will be adding power (from roughly 67% thrust to about 85%), whilst the Boeing would be going the other way. SignatureRead the latest aviation news at www.flight.org >> > Only aircraft that I've ever flown on which there may be an increase in >> > thrust is the A380. [quoted text clipped - 5 lines] > the AB will be adding power (from roughly 67% thrust to about 85%), whilst > the Boeing would be going the other way. Bit of a nonsense isn't it. To save say, 90 seconds of a higher power setting (which is low anyway) the takeoff is deliberately made more limiting from an accel/stop view point. Still, perhaps the runways used never come close to limiting at these weights. Cheers, >>> > Only aircraft that I've ever flown on which there may be an >>> increase in [quoted text clipped - 17 lines] > weights. > Cheers, Engines do sometimes suffer catastrophic failures that lead to accidents. It's rare, but it happens. There are also instances of accidents after non-catastrophic failures, for example BMA at East Midlands. The latter can be put down in part to pilot error, but they wouldn't have happened had the engine not failed. The less you run engines had high power, the lower the probability of such an event, whether during the high power run itself, or at some later time. So there is a safety benefit from derated takeoffs. Sylvia. >>>> > Only aircraft that I've ever flown on which there may be an >>>> increase in [quoted text clipped - 30 lines] > > Sylvia. Making every takeoff limiting increases the probability of a catastrophic accident in event of a Vef engine failure. Do you have any evidence that shows that fully certificated, properly maintained engines have a higher failure fate when using normal takeoff power than those using reduced power? I would guess that no such data exists. Reduced power takeoffs are used to save money in overhaul costs - the insurance company picks up the cost of overrun accidents. Cheers, >>>>> > Only aircraft that I've ever flown on which there may be an >>>>> increase in [quoted text clipped - 36 lines] > maintained engines have a higher failure fate when using normal takeoff > power than those using reduced power? No, but it seems self evident. Higher power puts higher stresses on engine components, making failures due to flaws more likely. In addition, things like fatique cracks will progress faster, and be more likely to cause failure before being detected during an inspection. Sylvia. >>>>>> > Only aircraft that I've ever flown on which there may be an >>>>>> increase in [quoted text clipped - 43 lines] > > Sylvia. A bit of speculation about the certification, manufacturing approval, and inspection/maintenance systems here, there is no point in pursuing these. Deliberately making takeoffs limiting increases the probability of overruns - there can be a myriad of reasons to refuse a takeoff. Despite the (very slim) safety margins built into the RTO I would be very surprised if an airline aircraft and crew will achieve the same distance as Boeing or Airbus with their flight test aircraft and crew, not to mention that they are permitted to average the results of a number of tests. While not the main reason for a number of recent takeoff incidents some would not have occurred if rated takeoff thrust was used. It all ends up being cost verses probability. Which is fine if one is never personally involved in an unlikely event. Cheers, , > A bit of speculation about the certification, manufacturing approval, and > inspection/maintenance systems here, there is no point in pursuing these. [quoted text clipped - 9 lines] > personally involved in an unlikely event. > Cheers, As long as you abort before V1, there should be no issue stopping within the available distance. Braking is handled automatically, and you will generally have some level of reverse thrust, which is not allowed for in the testing. There is plenty of margin in the 'go' case, and no need to push the power up to TOGA, unless you really want to. It's also a lot easier to handle the asymmetry. And, of course, if the conditions aren't nice, the use of derated thrust is always at the Captain's discretion. Full charge, when not demanded by the weight, can turn the aircraft into quite the handful, increasing the risk of tail scrapes, and making low level, level offs a somewhat uncomfortable affair. So, as I see, it there are pluses and minuses on both sides of the equation. SignatureRead the latest aviation news at www.flight.org > Is the thrust reduction during the climbout normal? I seem to recall this > happening, or had the perception of it occuring on flights that I've been on. Departing from Sydney 34R (third runway, towards the city). They'll often turn right, level off, and reduce thrust until they get out over the water. The pilot warns the passengers about it before takeoff. I've had it happen every time we use 34R on the way to NZ. Matt. > Departing from Sydney 34R (third runway, towards the city). They'll > often turn right, level off, and reduce thrust until they get out over > the water. The pilot warns the passengers about it before takeoff. > > I've had it happen every time we use 34R on the way to NZ. That pretty well describes all 767 departures off 34R. But, they aren't 'reducing thrust until over the water', even though that's how it looks. There is invariably a height restriction placed on that departure (haven't done it for a long time, but I think it was mostly 3000'). So, you need a lot less thrust to fly level, and at the max of 250 kias. SignatureRead the latest aviation news at www.flight.org >> Departing from Sydney 34R (third runway, towards the city). They'll >> often turn right, level off, and reduce thrust until they get out over [quoted text clipped - 7 lines] > done it for a long time, but I think it was mostly 3000'). So, you need a > lot less thrust to fly level, and at the max of 250 kias. Yeah, i know why they're doing it - it just happens that we're out over the water before climbing. Happened on my last Jetconnect 738 flight too. Big difference to the LAN A340-300 off 16R, that climb was so slow my ears didn't even pop. -- Matt. >>> Departing from Sydney 34R (third runway, towards the city). They'll >>> often turn right, level off, and reduce thrust until they get out over [quoted text clipped - 13 lines] >Big difference to the LAN A340-300 off 16R, that climb was so slow my >ears didn't even pop. As a result of certification requirements, the thrust to weight ratio on the ETOPS twins, especially the Boeing ones, is much much higher because you need to be able to 'fly away' on one engine, as opposed to 2 or 3 (tri or quad engine).. Typical A340-300 long haul GTOW ~610,000 pounds 4 X CFM56-5C3= 4 x 32,500 ~130,000 pounds 130/610= .213 767-300ER MGTOW 412,000 pounds 2 X CF6-80C2B6 =2 x 60,800 ~121,600 pounds 121,600/412,000=.295 777-300ER long haul TOW ~760,000 pounds 2 x GE90-115B= 2 x 115,000 ~230,000 pounds 230/760= .302 Whether your ears pop or not is more a function of the pressurization controller than actual rate of climb most of the time. While living in Phoenix AZ, there was a period when LH was operating an A340-300 PHX-FRA, it was an early afternoon departure, and during the summer months (typical temp 45C), it took that thing forever to climb... |
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