JulianUK From United Kingdom, joined Apr 2006, 105 posts, RR: 0 Posted (9 years 1 month 2 weeks 5 days 1 hour ago) and read 6208 times:
Where do you get the cost index setting you need to put into the FMC from? While I know that CI of 0 is for the most economical of flights and CI of 999 is for the most expensive but fastest of flight who is actually giving the pilots the number? Is it handed over before starting the flight?
VuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 1
Reply 1, posted (9 years 1 month 2 weeks 4 days 23 hours ago) and read 6195 times:
Quoting JulianUK (Thread starter): While I know that CI of 0 is for the most economical of flights and CI of 999 is for the most expensive but fastest of flight
Most economical/expensive its not quite what it is. CI 0 uses the least fuel but requires the longest time. CI 999 is the fastest and requires the most fuel. You have now time sensitive factors like cost of crew, cost of MX (time to next check - since flight hour based), A/C usage (you can fly more sectors per day if you fly faster) and leasing rate (if based on hours). The cheaper man power (or the higher the productivity of the existing staff) the more fuel prices play into the decision of the CI. In general, the higher the cost of fuel (in percentage) compared to the other houerly costs the lower the CI.
My company uses now 25 and we used to have 40 (a year ago) for all routes and it is usually determined by the performance department. Some other company uses diferent ones for different routes, however it is always on the first page of the computerized comany flight plans...
3201 From , joined Dec 1969, posts, RR:
Reply 2, posted (9 years 1 month 2 weeks 4 days 22 hours ago) and read 6191 times:
Some airlines pay a lot of money for consultants to study their overall costs and give them a single CI to be flown system-wide for all fleets. This seems questionable to me, since these flights are using many different fuel costs and have different economics of being late vs. early vs. on-time based on how delayed their departure is, how early/late in the day they are, whether they're inbound/outbound from hub, etc.
Some airlines use fixed hourly costs and the actual fuel costs of the departure station. This is better than a single value fleet-wide, but not clear how much better.
My experience from working with many airlines is that most of them don't really have a very good idea of what CI they should be using on any given flight. Airline costs are very complicated, and the costs based on time are usually non-linear given crew contracts, schedules to make, connections, next flights for the aircraft/crew, etc., not to mention slots vs. holding in some parts of the world. So maybe what they're doing isn't much worse than trying to do something better from flight to flight, and it's certainly a lot easier.
I guess that doesn't exactly answer your question. I think usually the CI value is standard either fleet-wide or by a combination of fleet and airport-pair or even individual flight, and not determined dynamically so it's just published as a standard operating procedure or a note to crew. There are generally stored notes given to the crew as part of their briefing, classified by the flight or the fleet or the departure airport or the airport pair, and the CI value to use is sometimes just one of those. When it is dynamically determined as part of the flight planning process, it is usually printed directly on the flight plan.
Thanks for the answers - never thought about this, faster the aircraft flies the less hours it will do therefore its maintenance check is delayed, however a faster flying aircraft will probably have more wear in terms of engines etc than a slow flying one - seems quite a contradiction!
Mcdu From United States of America, joined Apr 2005, 1544 posts, RR: 17
Reply 4, posted (9 years 1 month 2 weeks 4 days 9 hours ago) and read 6134 times:
Quoting JulianUK (Reply 3): however a faster flying aircraft will probably have more wear in terms of engines etc than a slow flying one - seems quite a contradiction!
Not neccessarily true. A airplane flying at m.86 versus m.80 is not straining the engines or the systems. A jet engine really relies on internal temps to make the difference in longevity and you for the most part must exceed the operating limits to damage the engine. It not like driving around town in your Honda with the Tach in the red to fly at or below the airplanes MMO. The engine really does not know the difference between the speeds. In fact depending on flight conditions you can have the engines on an airplane doing .80 indicating the same EPR/N1/EGT as the airplane doing .86.
As for CI rules, at my company a struggling US legacy carrier that has just emerged from BK, we have a revised CI posted regularly based on the company fuel cost. They provided us with two numbers, early or late. Domestically an early ETA will drive us to the lower CI to save fuel and arrive on time. Often if we arrive too early the stand will be occupied with another aircraft and we spend the time in a holding area on the ramp waiting for a gate. On the international sectors you find yourself married to a specific mach number to maintain the required spacing on the tracks. Therefore the CI goes away and you will see often the plane flown in selected Mach to prevent the airplane from slowing as it gets lighter.
CX flyboy From Hong Kong, joined Dec 1999, 6705 posts, RR: 55
Reply 5, posted (9 years 1 month 2 weeks 4 days 5 hours ago) and read 6114 times:
On the 777, we normally fly at CI60. If we are running late and time is important then the company can issue us with a CI250 plan. Anything more than this burns up too much fuel to be worth it. If we are running ahead of schedule, then we slow down to CI20. Any less than that and as previous posts mention, maintenance costs can go up more.
As for the engines working harder but less time v.s less fuel but more time, it also depends on the deal that the aircraft has with the engine manufacturer, or whether they own their own engines. Some companies lease engines by time used inflight and therefore it may be in their bests interests to fly faster and pay less. maintenance costs within reason may be irrelevant to them. On the other hand, an airline might own their own engines and want to save wear and tear. it really depends.
Pihero From France, joined Jan 2005, 4916 posts, RR: 78
Reply 7, posted (9 years 1 month 2 weeks 4 days ago) and read 6074 times:
For those interested, this is a paper by the IATA via Airbus.
One of my bibles ! Getting to Grips with the Cost Index
It will answer all your questions and a lot more, like for instance how to obtain max rate of climb.
And it will do away with some misconceptions about the 340, too.
Pihero From France, joined Jan 2005, 4916 posts, RR: 78
Reply 9, posted (9 years 1 month 2 weeks 3 days 23 hours ago) and read 6058 times:
You'll love that one, and I have a few more for you when you're finished !
Actually, it's full of pragmatic sense, not maths and the flight operations bit won't have any more secret for you.
Your return date on my message board,pretty please ?