Hi,

Just wanted to share some info.

I recently flew a few short real life flights (passenger) with Scandinavian. ENGM-ENBR and ENGM-ENVA.

I noticed a marked difference in flight behaviour during takeoff, with acceleration at 1500, not decel. Also very high power in TO (maybe) and CLB (for sure). I decided to ask a pilot, and it turns out fuel is now so expensive that the first priority is to get high up FAST. This will potentially add engine maintenance cost, but it is still judged to be a smaller expence than the fuel.

I did not get to ask particulary about derate, but I am quite sure there is no derate at CLB. Maybe TO-1.

The cost index for Scandinavian 737 is now 5.

Hope this is of interest.

 

Regards,

Andy

Would running the engines at full thrust for only a few seconds after takeoff really save that much fuel? I thought the lower fixed thrust settings were used to make overall flight more efficient (of course only if weights are appropriate). With full thrust at all times, I would imagine that the engine costs would outweigh the fuel saved, if any.

All data I have seen for 737s are in agreement that using full TO thrust for shorter time uses less fuel in greater picture than using reduced thrust for longer time.

 

Now the thing is, in aviation, it is no longer the norm, that airlines own aircraft, engines, brakes, et cetera.

There is a very common arrangement in place now called "power by the hour", which basically means, that airlines rent engines from another entity (most often the engine manufacturer), and the engine owner is responsible for engine maintenance.

 

Now considering, that derates are mainly about lowering maintenance costs, it might be, that SAS has a power-by-the-hour contract with CFM, without any kind of incentive scheme to use derates, and so in the end it makes more sense for them to "trade the engine life for fuel".

 

 

Interestingly enough, there is a study somewhere, that came to a conclusion, that on Airbus A320s, derate actually lowers total fuel consumption....

Interesting. It would be cool to see some fuel consumption graphs comparing various takeoff thrust settings, acceleration altitudes, and climb thrust settings. The Airbus derated thrust data/logic seems more logical to me. Perhaps I should test the fuel consumption properties of Boeings in FSX.

I can't speak for all airlines, but given the access I have to airlines in the groups I work with I can tell you CI is highly variable.

 

Was the flight delayed? It gets bumped up.

Is there a flow program to the destination airport? It gets bumped down.

Additionally, there are other factors that influence it.

 

Granted, there are several airline SOPs that say "if we don't specifically state otherwise, use X," but it's not as constant as you'd think.

 

Why do I say all of this?

Specifically because we're talking about SAS, and because ENGM uses Point Merge, which uses required time of arrival (RTA). Cost index is somewhat of an idea of balancing time-related costs with fuel-related costs. The idea is that, with a lower CI, I don't mind getting there later if my fuel consumption is lower. The problem is, flying into ENGM, you get assigned an RTA that says "you have to be at this fix, at this time." In order to meet RTAs while still considering econ factors, a lot of the systems modulate the CI for you to meet the RTA (you can read more about it here).

 

I'm not sure how SAS has implemented this precisely, but CI is meant to be variable, and it is definitely variable in the cases of trying to meet an RTA.

 

For those of you Stateside, RTA is something to learn about if you haven't already.

Hi,

"if we don't specifically state otherwise, use X"

Yes, it seems to be like this. I was on a delayed SK flight today, and it felt like no derate at all, and speeding at crz.

On a flight a week ago, I asked the pilots. They basically confirmed my first post here, with a standard CI of 6. They used derate TO-2 and +50 deg OAT. Then CLB with no derate to get fast to crz and save fuel.

I did model this in FSX with a 700 departing ENGM. I got N1 77% at TO, increasing to 90-ish (dont remember precisely) at 1500ft. This is exactly the way it felt as a passenger in real life , based on sounds and general behaviour of the acft.

 

Regards,

Andy