---
title: How Air Caraïbes boosted fuel savings through idle factor optimization| OpenAirlines
description: See how Air Caraïbes and French bee cut fuel burn 15.5 kg per flight with idle factor optimization, with zero impact on pilots or flight time.
image: https://blog.openairlines.com/hubfs/Header_case_study_idle_factor_ai.png
---
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# Idle factor case study: how Air Caraïbes saved 55,000 kg of fuel
Published by [Guillaume](https://blog.openairlines.com/author/guillaume) on Nov 13, 2026, 10:39:45 AM
Air Caraïbes Atlantique and French bee found 55,000 kg of fuel savings hiding in a Flight Management System parameter most Airbus operators leave at zero: the idle factor. Here’s the full story of how they did it, from a controlled trial to proven results.
| 📊Summary Air Caraïbes Atlantique and French bee, two sister A350 long-haul operators, optimized the FMS idle factor across their 12-aircraft fleet. A 1,500-flight controlled trial demonstrated 15.5 kg of fuel saved per flight per 1-point reduction in idle factor, with no impact on pilot workload or flight time, and achieved regulatory clearance in two days. - [What is the idle factor, and why does it matter?](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#what-is-idle-factor) - [The trial: a rigorous, staged rollout](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#the-trial) - [The results: what idle factor optimization delivered](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#the-results) - [Why idle factor has to be tail-specific, and refreshed every month](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#tail-specific) - [Does it affect flight time or pilot workload?](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#flight-time-pilots) - [How Air Caïbes and French bee implemented the process](https://blog.openairlines.com/idle-factor-case-study-how-air-caraibes-french-bee-saved-55-000-kg-of-fuel#implementation) - [Idle factor optimization savings simulator](https://www.openairlines.com/idle-factor-fuel-savings-simulator/) **Looking for more details on this case study**?[**Download the PDF**](https://info.openairlines.com/idle-factor-case-study-air-caraibes) |
| --- |
## What is the idle factor, and why does it matter?
As explained by our experts in [this article](https://blog.openairlines.com/idle-factor-optimization-fuel-savings-hiding-in-descent), the idle factor is a Flight Management System (FMS) parameter for Airbus aircraft. It adjusts the idle descent slope computed by the FMS, so the flight path matches the aircraft's actual performance rather than a generic model.
For many Airbus operators, this field sits at zero for years.
Air Caraïbes Atlantique and French bee, two sister A350 long-haul operators based in Paris Orly, saw this parameter as an opportunity to save fuel. They lacked a clear read on its potential and a safe way to validate it, so they partnered with OpenAirlines to explore the topic through SkyBreathe®.
## The trial: a rigorous, staged rollout
Before committing, the two airlines wanted a 360° view: fuel savings, safety, pilot workload, and fit with existing workflows. That called for a controlled trial, not a quick switch.
Two design choices made the trial rigorous:
- **Real operations, at scale:** the whole A350 fleet (12 aircraft across 3 subtypes) ran the trial over 4 months and roughly 1,500 flights.
- **A staged, comparative rollout:** OpenAirlines modeled each aircraft’s own data and recommended a tail-specific value, then the fleet split into 3 groups to isolate the real effect from seasonal variation or other noise.
Air Caraïbes Atlantique and French bee did not need to run the modeling themselves. OpenAirlines handled the science, comparing book performance from Airbus PEP against real Flight Data Recorder (FDR) data, and delivered final values ready to use.
## The results: what idle factor optimization delivered
| 15.5 kg of fuel saved (~34 lbs) on average, per negative idle factor point. | The trial produced a clear, measurable answer: **15.5 kg of** fuel saved per flight, on average, per negative idle factor point. > *“That means if your idle factor is minus 2.0, you can expect 31 kg per descent. That’s based on all the FDR data analysis we conducted.” > Clément Cibot, former Head of Flight Operations Engineering, > Air Caraïbes Atlantique / French bee* |
| --- | --- |
Once the optimized values went live across the whole 13-aircraft fleet in May 2025, that per-flight gain turned into fleet-wide numbers:
| Metric | Result |
| --- | --- |
| Fuel saved, whole fleet, 8 months of 2025 | 55,000 kg / 121,254 lbs |
| Fuel saved, whole fleet, 12 month extrapolation | ~83,000 kg / ~183,000 lbs |
| Fuel saved, per aircraft, 12 month extrapolation | ~6,400 kg / ~14,110 lbs |
In context, idle factor optimization adds 4 to 5% in fuel savings on top of every other best practice Air Caraïbes Atlantique and French bee already apply through SkyBreathe®.
## Why idle factor has to be tail-specific, and refreshed regularly
The trial surfaced two findings that shaped how Air Caraïbes and French bee run idle factor today.
**First, the idle factor varies widely between tails**, even within the same subfleet. Each aircraft ages and degrades differently, so a single fleet-wide value cannot fit every tail well.
**Second, idle factor drifts for the same aircraft over time.** Engine age, maintenance events, shift performance, and a value accurate at delivery slowly fall out of step with reality.
See the per-tail and seasonal variation charts in the case study PDF. Download it here.
| 💡**Pro tip:** that is why Air Caraïbes and French bee treat idle factor as a routine, not a one-time project. Refreshing each tail’s value every month keeps it matched to the real aircraft, so the gains hold and do not quietly erode. |
| --- |
## Does it affect flight time or pilot workload?
No. The project measured this directly, and the answer on both counts is no.
**Flight time:** the impact was negligible (under 1 minute).
**Pilots:** the airline analyzed pilot feedback closely over the trial period through safety reports. Nothing changed in how pilots fly. No impact on the approach, the spoilers, or any procedure.
| > *"For pilots, it’s pretty easy to take into account. It doesn’t change anything in the way they fly the aircraft. It doesn’t impact the approach, the spoilers, nothing. When we asked them, they were not disturbed at all.”* Clément Cibot, former Head of Flight Operations Engineering, Air Caraïbes / French bee |
| --- |
There are even upsides for pilots. A better calibrated idle factor places the Top Of Descent closer to the aircraft’s actual behavior, which makes the descent path easier to fly. And when the FMS model matches reality, pilots trust flight planning more, which matters for long-haul operations and discretionary fuel decisions.
## How Air Caraïbes and French bee implemented the process
Three teams needed to be aligned: Maintenance, who update the FMS; pilots, who need to know the current value; and Flight Ops Engineering, who needed a process light enough to run routinely.
The answer was to fold idle factor into a workflow the airlines already ran: their existing monthly process for updating the fuel performance factor.
Learn more about the implementation process of the idle factor initiative at Air Caraïbes in the case study PDF.
| 💡**Good to know:** The idle factor recommendation engine is built directly into [SkyBreathe®](https://www.openairlines.com/aircraft-performance-monitoring/), where it updates daily for every aircraft. Flight Ops Engineering teams get full autonomy to pull the values when they need them, including outside the monthly routine, for example, right after an engine swap. |
| --- |
What about authorities notifications?
In France, the civil aviation authority is the DGAC. A change like this needs formal notification: a Change Notification Form, a Safety Assessment, and a clear description of what the airline intended to do. Air Caraïbes Atlantique and French bee’s Flight Ops Engineering Department prepared that dossier, and the DGAC acknowledged it within 2 days.
## To sum up
The numbers make the case: 15.5 kg (34 lbs) saved per flight per negative idle factor point, about 83,000 kg a year across a 13 A350 fleet. That figure reflects conditions at launch. Idle factors drift upward over time, so keeping that level of savings depends on regular recalibration, which is exactly why Air Caraïbes Atlantique and French bee run it regularly.
In other words, idle factor optimization is an airline fuel-saving initiative easy to implement that comes with no trade-offs: no impact on flight time, no impact on safety, no impact on pilot workload.
| Stakeholder | Impact |
| --- | --- |
| Flight Ops Engineering & Maintenance | Idle factor updates fold into the existing monthly fuel factor workflow, with one combined task for maintenance. |
| Pilots | No added workload: one more value to cross check in the EFB app, alongside the fuel factor they already check. |
| Scheduling and disruption management | No change to flight time, so no impact on on-time performance. |
| Regulatory clearance | DGAC acknowledgment in 2 days, backed by accurate, trustworthy data. |
**Want to go further?**
**Download the case study PDF** to get the details on model development and trial scope, charts on idle factor fleet distribution & seasonality and how the airlines implemented the new initiative.
Download the case study
| About the authors: meet the experts behind this study [**Clara Riffaud**](https://www.linkedin.com/in/clara-riffaud-440ba0145/) Head of Flight Operations Engineering Department at Air Caraïbes Atlantique and French bee and member of the Green Team. I have worked for six years - one year in the Safety and Compliance Department, followed by five years in the Flight Operations Engineering Department, where I have been the Head since 09/2026. **[Clément Cibot](https://www.linkedin.com/in/cl%C3%A9ment-cibot-8a3326116/)** Former Head of Flight Operations Engineering Department at Air Caraïbes Atlantique and French bee and member of the Green Team, transversal team dedicated to the development of environmental projects. I have worked for five years at the Operational Control Center, first as an engineer and then as Head of the Flight Preparation Department. I have then joined the Flight Operations Engineering Department as a Manager since 2023. **[Guillaume Dumas](https://www.linkedin.com/in/guillaume-dumas-19626012a/)** Guillaume, Product Manager at OpenAirlines, leads the development of Aircraft Performance Monitoring (APM) capabilities within the SkyBreathe® platform. An ISAE-SUPAERO aerospace engineer, he combines strong aviation expertise with more than eight years of experience at OpenAirlines. |
| --- |
---
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---
##### FAQ
How much fuel can idle factor optimization save?
At Air Caraïbes and French bee, idle factor optimization saved 15.5 kg (34 lbs) of fuel per flight per negative idle factor point, averaged across all flights (A350).
Tags: [Aircraft performance monitoring](https://blog.openairlines.com/tag/aircraft-performance-monitoring), [Technology](https://blog.openairlines.com/tag/technology), [Fuel program](https://blog.openairlines.com/tag/fuel-program)
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