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Mixed-Fleet Flying


Mixed-fleet flying of a group of airplanes allows the operator to use the same pilot group to fly all airplanes in the group. This can save the operator money in retraining pilots for other airplanes and in ensuring pilots are able to fly the new airplane when a change of equipment is dictated due to maintenance or other issues. Mixed-fleet flying has historically been approved for different models of the same airplane type; however, recently questions are being raised as to whether it may be safe and economically advantageous to mix other airplane types.


We are part of a team that is evaluating the safety and effectiveness of possible mixed-fleet flying of different types of airplanes. The question is being addressed from all angles and we have all interested perspectives on our team. Our primary part of the challenge has been to develop an assessment methodology to identify potential vulnerabilities for pilot error when the airplanes are being mixed and to communicate that to the rest of the team as we consider all aspects of the question.

Approach and Solution

We began with a comprehensive list of tasks that would be performed by pilots in both airplanes. An analysis was then accomplished for each airplane to determine the information that would be used to perform each task and the actions required to perform the task and how specifically they would be performed in each airplane. The information gathered was then analyzed for performance vulnerabilities in situations when the pilots would have habits formed in one airplane and then be required to fly the other airplane. The list of potential vulnerabilities resulting from this assessment was then used to help develop objectives for a full-flight simulator study in which we included scenarios and maneuvers that would verify the existence and criticality of the vulnerabilities. The pilot performance in all of the simulator sessions was video taped and we analyzed the video tapes to determine the specific effects of mixing the airplanes on pilot reaction time for particular critical actions. The simulator study also provided pilot performance to be evaluated by our full team, including Boeing and the FAA, for expected performance and proper use of the airplanes. The team is working together to develop final recommendations about whether and how the airplanes can be mixed by airlines in the future.


The results of the simulator study and our analyses are currently being reviewed by the FAA and manufacturer to develop guidance documents for the mixing of the two airplanes by airlines in the future. We will be involved with Boeing and the FAA in a mixed-fleet flying evaluation of another group of airplanes in the near future and will be able to use that same methodology that has proven to be effective in the study just completed.

Funding Agency:

Federal Aviation Administration (FAA)

Project Partners:

Federal Aviation Administration (FAA), a major airline, Boeing Commercial Airplanes, and University of Illinois (UI)

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