AIRCRAFT PERFORMANCE LEVEL REVIEW

Distinguishing nominal & baseline performance and in-service performance

 

By Jean-Jacques Speyer

 

1. INTRODUCTION

 

This subject needs to be re-addressed as some recent evolutions in our business procedures mandate clarification. Fixing cruise performance is a policy matter depending of several factors which can change throughout time: this leads to the IFP-level. Throughout the years Airbus Industrie has been in three typical product life cycle situations that will be schematized in the following graphs. Distinguishing delivery performance and in service performance is essential not to confuse "perceived" specific range degradation from "real" deterioration. Real deterioration processes are naturally occurring throughout any aircraft / engine life. These can be attenuated (cost benefit analyses prevailing) by investing in engine maintenance (1% SR / 10°C EGT)
and to some extent into aerodynamic maintenance (brochure).

 

Initially, we were adopting a policy based on expected engine improvements which finally have not been fully achieved. These optimistic stances existed for the following case examples:

 

- A300-622R/PW4158

IFP 92 below nominal level as Phase III engines not as initially planned,

- A300-605R/CF680C2: IFP degraded in 92 by 1%,

- A310-204/304/308/CF680C2A2/A8: IFP 91 degraded by 1% in 92

- A310-324/325/PW4152/56/56A:

IFP 91 degraded by 0.8% as Phase III engines short

- A320-211/212/CFM56-5A1/A3: initial shortfall in SFC planned to be remedied in 2

steps, but not achieved; a too optimistic IFP was degraded in 1996.

 

Subsequently, a « long-range » caution policy was adopted as there was a definite need not to misestimate specific range with longer range aircraft or with aircraft that would be operated at the full extent of their payload range. Case being for example :

-A319-113/114/CFM56-5A4/A5 : nominal level 1% above IFP

-A320-232/233/V2527(E)-A1/A5 : A1 & A5 very close ; nominal level as IFP 89

-A321-131/231/V2530-A5 : nominal level 0.8% above IFP 93

 

Presently, a conservative « realpolitik » has been adopted: a conservative stance with aircraft usually on IFP or 1% better than IFP to be sure to absorb initial in-service deterioration. This is exemplified with the following cases:

 

- A330-301/CF6-80E1A2 : nominal 1% better than IFP

- A330-321/322/PW4164/68 : nominal close to IFP

- A330-341/342/Trent768/772 : nominal.5% above IFP

- A340-313E/CFM56-5C4 : nominal 0.5% above IFP

 

2. RATIONALE FOR FIXING BASELINE PERFORMANCE

 

The following figure says it all. By becoming more conservative we avoid the difficulty of the opposite policy : to be faced with a perceived in-service deterioration that largely consists of apparent deterioration and not just of real genuine deterioration. Of course, at present we have a buffer that would absorb initial deterioration for some time before this would really become apparent.
But numerous audits throughout the years –even in the absence of real deterioration steered us towards

The conservative stance now adopted.

 

 

3. PERFORMANCE MONITORING

The methods developed throughout the years need to be reviewed properly when addressing the subject. A short review is given in the paper both for newcomers to Airbus as for others.

 

We recommend using the Aircraft Performance Monitoring Program with the recording techniques as specified by Airbus, with data processing by dedicated programs (APM/IFP) and critical data analysis. Doing the job in the airline itself sometimes without calling from assistance from the manufacturer will breed experience so as to better discuss with our experts subsequently.

 

With regard to actions to undertake we recommend to identify priority one-time or
periodic maintenance checks and tasks for Performance Retention and Recovery. This also breeds know-how and experience and can be very cost effective. A brochure on aerodynamic deterioration exists to that extent. Engine manufacturers also maintain comparable programs.

 

4. CONCLUSION

In conclusion, we would rather ask the airlines to express their viewpoints and reactions centered around the following questions. Please provide us some insights as to what the average fleet cruise performance levels are compared to your in-house airline baselines.

feel free to quote levels as known by you!

 

do you establish your own delivery baseline?

 

do you perform periodic performance monitoring?

 

do you practice trending for this?

 

do you refer to the IFP?

 

do you reflect this in the performance factor?

 

do you work with ECM ?