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Aviation History
1990
1990 - 1358.PDF
LETTERS Fuel fallacies SIR—It is my belief that the world's airlines, if they are oper ating modern Boeing aircraft in accordance with the manufactur er's guidelines, are probably flying their aircraft at the wrong speeds. The same is probably true for other aircraft from other manufacturers that carry a flight management computer (FMC). The pilot can programme the aircraft route and other parame ters into the FMC. The computer can then determine the best height and speed for the aircraft to fly. One such parameter is the cost index (CI). This can best be understood as a balance between fuel costs and other operating costs. When fuel is cheap, an index for cheap fuel is pro grammed into the FMC, and the aircraft will fly (slightly) faster, burning more (cheap) fuel, but saving on other operating costs (engineering time, crew allow ances etc). The examples below assume an aircraft flying a series of flights between points A and B. Conditions are still air, and the same departure and reserve fuel is required at either end of the route. Example 1A The CI for both 3h jlight time, departure points 10,000kg burn is 25, giving a A •''B round-trip fuel burn of 20,000kg Example IB and 6h flight 3h flight time, time. 10,000kg burn AM B (The cheaper the fuel the higher the numeric value.) Example 2A Cheap fuel CI of 2h55min flight 35. time, 10,200kg burn A •B The CI for cheap fuel gives a shorter flight time but increased burn. Wl NG LETS SWARF TO BLAME SIR—P Phillips referred to the Canberra encountering trim problems in its early days (Let ters, 31 Jan-6 Feb). I was an RAF engine fitter at that time and recall several aircraft re turning from sorties with re ports of runaway tailplane trim problems. The solution was simply to improve quality control: metal swarf had been finding its way into the con sole contacts and shorting out the relays, causing involuntary selection of degrees of trim. MR BARHAM, Calne, Wilts UK LICENCE VALUE SIR—In response to K D James' letter 21-27 March), I can hardly blame German Cargo for refusing to hire Brit ish-licensed crews. I am Brit ish, but hold a US FAA licence. If a government agency thinks that certificating a simulator to UK CAA standards is worth some £9,500, and each year a licence renewal is worth some £4,500, it is living in Wonder land. The fee the FAA charges is considerably different: it's free. DAVID MACDONALD, Frankfurt, West Germany FIELD'S CAPABILITIES SIR—The Third-Party Main tenance Directory (Flight, 10- 16 January) contains some dis crepancies concerning Field Airmotive's capabilities. It is FAA and CAA approved, and overhauls and repairs T55 and T56 engines plus the others mentioned. LYN STEVENS, Field Airmotive, Croydon LOGGING EXPERIENCE SIR—As a pilot's assistant for a small UK airline, I am not permitted to log hours flown on scheduled services. An air craft without a serviceable autopilot cannot fly unless there is at least a PPL with an IMC rating—a legal require ment to relieve the captain of the high workload. The Civil Aviation Authority states that, although I have a B rating, I must possess at least a com mercial licence to log the flight time, yet I perform the same "non-handling" duties as a fully qualified copilot and have almost 600h total time. My captains believe my experi ence merits logging at least 25% of the flight time. SA BOWEN, Dorset Example 2B Expensive fuel CI 3h 5min flight time, of 15. 9,800kg burn A< B The expensive index gives a longer flight time but a decreased burn. The crucial point to note is that at point B (where fuel is expensive) an uplift of 10,200kg is required before the aircraft can depart for A. At A, an uplift of 9,800kg is required (although we have already determined that fuel at A is cheap). Using current methods, more fuel is being up lifted where fuel is expensive and less fuel where it is cheap. If we cannot burn our cheap fuel, the correct method of deter mining the CI is by entering the replacement cost of fuel. If the fuel at the next uplift point is expensive, then the CI for the next uplift point should be en tered into the FMC. In the example above, swap ping the CI at A and B will give the same total burn, the same flight time, but more fuel will be uplifted at the cheaper point. There are, in theory, occasions when advantage can be taken of cheap fuel to fly that bit faster. If departure fuel can be adjusted so that the burn does not affect the uplift, then it is acceptable to burn the cheap fuel—if the land ing weight is restricted to 90,000kg. At A, 10,200kg can be put in, allowing the aircraft to fly slightly faster to arrive at maxi mum landing weight. The burn does not influence the uplift be cause of the need to get down to maximum landing weight. In practice, we can never be accurate concerning landing weight, and most pilots would allow themselves a buffer of about 500kg to ensure arriving at below maximum landing weight. I would be pleased to hear from anyone who can demon strate that I am wrong to state that the CI should be determined by the cost of replacement fuel, not, as is done currently, the cost of departure fuel. P HOMER 24 Grange Park Avenue Wilmslow Cheshire SK9 4A] The right place for Dakotas SIR—All that gleaming new tarmac in the picture of Dakotas in 1946 (Letters, 28 March-3 April) makes me suspect that they are not at Hendon, but Northolt. The fact that the nearer Dakota passed from BOAC to Northolt-based BEA that year hardens my suspicion. I will even stick my neck out and suggest also that the picture was taken at the time when aircraft at North olt parked facing away from the terminal buildings (rather than alongside, facing west), and that the photographer is looking to wards South Ruislip. GEOFFREY NEGUS 2 Heathcote Ave, Solihull West Midlands Finnair'sDC-10 link to Japan SIR—The Finnair service ' to Tokyo (Letters, 28 March-3 April) began on 22 April, 1983 (not 1984 as stated). Extra fuel tanks help the DC-10-30ER cover the 11,025km stage length via the Bering Strait. JOHN WEGG "Airliners", PO Box 1439 Pollock Pines CA95726-1439,USA The extended-range variant of the DC-10-30 helps Finnair fly further 71 FLIGHT INTERNATIONAL 9-15 May 1990
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