Gambling with fuel The Scandinavian Airlines (SAS) fuel scare (Flight International, 22-28 June) illustrates that a flightplan is a forecast and that the flight management computer (FMC) operates in an international standard atmosphere (ISA) world. Its predicted optimum altitudes are only correct in that world, when the ISA temperature lapse rate and the ambient static air temperature (SAT) coincide. My rule of thumb is to reduce the displayed FMC optimum altitude by 100ft (30m) for every 1°C that SAT is above ISA. This is strategic tactical cruise management. When an overburn becomes evident, it is essential to manage it with FMC cost index intervention to arrest this underplan. In the flight-planning phase, consider the US Federal Aviation Administration's FAR 121.645, where fuel reserves are: (a) the sum of 10% of the fuel burn calculated at the time and altitude existing at the end of the flight; (b) 30min holding at 1,500ft (c) the fuel burn to the most distant alternate. On a Washington-Paris flight of 8h, 10% is 48min. For economy, release the flight to Shannon via 15 West. Upon reaching this "reclearance fix", the dispatcher and crew would "reclear" to Paris, all being well. If not, land short at the original "release" airport of Shannon. In this case of 15 West to Paris of 90min flying time, the 10% contingency rule now only requires 9min of cruise fuel instead of 48min. This is gamble-free gambling. Combine still air regulations and ISA FMC predictions with blind faith in a blind landing and one has the makings of a very "fuelish brew" indeed. David Connolly Brussels, Belgium
Mad idea? I know this sounds barking, but if the USA wants a heavy vertical take-off and landing (VTOL) transport, why not take a British Aerospace 146-100/RJ70, remove its ALF502/ LF507 engines and replace them with Rolls-Royce Pegasus 11-61s? The empty weight of an RJ70 is quoted as 24,000kg (53,000lb) with a maximum take-off weight of 38,000kg standard or 43,000kg optional. Four Pegasus 11-61 engines should produce a combined thrust of 95,200lb (425kN). Like the BAe Harrier, it would operate best in short take-off vertical landing (STOVL) mode. BAe demonstrated a sideloading tactical airlifter version of the 146 around 1989. A STOVL version of this would be an awesome special forces transport or carrier delivery aircraft. John Hartley Woking, Surrey, UK
Productivity and flightcrews One factor which does not seem to feature in the current debate concerning European flightcrew duty limitation regulations is the effect on productivity caused by excessive duty hours and "creative crewing". In the early 1980s the training department of the UK charter airline I was flying for calculated that the cost when one pilot left for another employer was about £20,000 ($37,000) - the figure now must be at least double. A constant turnover of pilots means a greater requirement for training staff, and so on. It is interesting to note that you quote Michael O'Leary, chief executive of Ryanair, referring to pilots as "the most cosseted group of employees in the world" since it is the low-cost airlines that will feel the economic effects of pilots moving elsewhere more than most other operators. Many younger and less-experienced pilots regard the low-cost airlines as merely training grounds to enhance their future careers. Who can blame them? Robert Taylor Nottingham, UK
Facts and fatigue Much of the debate over flight duty time limitations is being carried out in the absence of any direct or scientific measurement of fatigue. An objective measurement of an individual's level of physiological fatigue can be made and recorded quickly, based on well-established medical criteria using a product like Advanced Aviation's Eyecheck that measures the physiological response of the eye, using simple and meaningful criteria for directly measuring fatigue levels. Kim O'Neil Managing Director, Advanced Aviation Technology Compton, Surrey, UK
D-Star puzzle D-Star's nested gas turbine can certainly be described as innovative (Flight International, 8-14 June) and, as with all innovative proposals illustrated by patent diagrams, raises more questions than answers. Compared with a "standard layout", the most obvious problem is the loss of ability to modify engine sections individually, for example measuring top speed by simply increasing diameter. The heat exchange is there simply to facilitate crossover between inlet and exhaust air and as shown would be of little value as a heat exchanger. No indication is given as to how the fuel-control system interfaces with the engine or how it would be driven. Similarly, how is an electrical supply provided? D F Newland Stanmore, Middlesex, UK
Source: Flight International
