Hi I have a few minor questions. First off, in real life, do commercial jet airplanes (Boeing, etc.) have their instruments indicate units in British Imperial? (altimeter in feet, airspeed in knots, temperature in fahrenheit, fuel in pounds, pressure in inches of mercury) OR are the instruments a mixture of British Imperial/Metric? If so which instruments indicate which standard?Furthermore, if altitute is indicated in feet, is this an international standard? Do they use feet in altimeter in Europe? If not, how do they work around flight levels being that one is in meteres and the other is in feet?My second question can, I guess only be answered by retired airline pilots. I know that an airplane, upon landing at its destination must have a certain amount of fuel in reserve in case it had to execute a missed approach/fly the holding pattern for whatever reason. Now I'm sure today's airlines have complex computer programs which take into account the weather en route, winds aloft, traffic jam on the taxiways, passenger load, etc. to precisely calculate the amount of fuel needed for the flight. However, do airlines go as far as to tell the pilots the cruising altitude for their flight? Do airlines tell pilots what cruise speed to fly? Do they tell them at what rate they should climb? In other words, how much direct interference does an airline have over a flight and the pilot who flies it?Thanks a bunch beforehand.

Just remember: PIC *always* has the last say, so even if one's airline says to fly a route a specific way doesn't mean the PIC can't deviate from that route if he believes an alternate route would be better.-Max Cowgill

>do airlines go as far as to tell the pilots the cruising altitude for their flight? Do airlines tell pilots what cruise speed to fly? Do they tell them at what >rate they should climb? Hi, the short answer is yes. Every part 121 air carrier flight must be 'released' by a Dispatcher. The dispatcher's job is to plan the flight in its entirety, including the route of flight and fuel requirements among other things.The fuel issue is a complicated one...first you must figure out the planned enroute fuel burn (This is affected by many things, like cruise altitude, mach speed, route of flight, winds aloft, etc). Then you have to add fuel for taxi in and taxi out, adjusting for anticipated delays. Fuel must then be added for any anticipated airborne holding, and if the destination required an Alternate, you must also add fuel to fly to the farthest alternate. All air carriers on an IFR flight plan must also carry an IFR Fuel Reserve. The required fuel reserve changes depending on what kind of operation you fly (Domestic, Flag or Supplemental), and where you're flying from/to (Domestic or International). My experience is limited to US Domestic operations, so thats what i'll talk about... In addition to all the other fuel requirements, we're required to carry enough fuel to fly for 45 additional minutes. When you add up all those values, you get a minimum fuel value or 'Min Fuel'.On top of Min Fuel, we add 'Contingency Fuel' which provides the crew some flexibility if ATC issues an amended clearance, or if the crew needs to deviate for enroute weather, or any other unforseen problem. This fuel is not 'required' and is considered 'extra' fuel.The result for a CRJ looks like this:B/O 3467 Enroute BurnoffTAXI 300 Taxi In/OutALT 1253 Required Alternate FuelHOLD 1000 Required Holding FuelRESV 2000 45 minute IFR Reserve-----------MINF 8020 Minimum Legal Fuel to depart-----------CONT 1000 Contingency or 'extra' fuelPLND 9020 Planned Fuel LoadTo arrive at these numbers, we must control things like altitude and airspeed. So when its all said and done, we provide a dispatch release to the crew that specifies a cruise Flight Level or altitude, a cruise Mach or airspeed, and a profile for climb and descent. For instance, my company uses a set climb profile of 250kt/.70 mach, and a set descent profile of 290kt/.77 mach. Of course, its rare to actually fly the profile, as ATC is asking you to do something else...>In other words, how much direct interference does an airline have over a flight and the pilot who flies it?A lot actually. But its not so much the 'airline' as it is Dispatch and, to some extent, Maintenance Control. We operate under the concept of 'Joint Operational Control'. This means that as a dispatcher, I am jointly responsible with the PIC for the safety of the flight. As such, I can reroute the flight, divert the flight, ground the airplane, and even declare an emergency. Its very rare to have to excercise any of these authoritues, though. Hope that answers some of your questions...Best Regards,Nicholas LandolfiBlue Ridge DxEDITED at 1837z for spelling

Excellent informative post, Nick.Peter Sydney Australia

do commercial jet airplanes (Boeing, etc.) have their instruments indicate units in British Imperial? (altimeter in feet, airspeed in knots, temperature in fahrenheit, fuel in pounds, pressure in inches of mercury) OR are the instruments a mixture of British Imperial/Metric? If so which instruments indicate which standard?Furthermore, if altitute is indicated in feet, is this an international standard? Do they use feet in altimeter in Europe? If not, how do they work around flight levels being that one is in meteres and the other is in feet?Outside North America, a mix of Imperial and metric is used. Feet is the standard unit for altimeters in most of the world but there are some countries - Russia, I think, is one example - that still use metres. Some modern altimeters are switchable between feet and metres but otherwise, a suitable conversion chart giving flight level/metric equivalents must be used. The knot is the general world unit for airspeed but again there are a few countries that use kph. Outside North America, the degree Celsius is universal for expressing temperature and visibility is expressed using metres/kilometres although actual distances are more usually expressed in nautical miles.Again outside North America, the standard unit of pressure is the Pascal with altimeters using the hectoPascal. Some countries - the UK for example - still use the milliBar but for all practical purposes 1 milliBar = 1 hectoPascal so they're considered to be the same. When moving from an area using hPa or mB to one using in/Hg, either a switchable altimeter or a conversion chart is used.Pete