How can you build up a robust schedule in Flight Scheduling? (Part 1 of 3)

How do you balance punctuality vs. productivity? Within this joint three-part blog sequence my three colleagues and I share five approaches towards minimizing propagated delays and increasing aircraft utilization by robust scheduling.

Lufthansa Systems Blog

A robust schedule is the be-all and end-all of an airline: It defines its product, its revenue potential and also its operating costs. The Scheduling Management department determines within the Flight Scheduling process where and when the airline will fly respecting all operational and commercial constraints. The challenge thereby every Flight Scheduler faces is well known: You have to outsmart the competitors, fulfill market demands by offering the right flight times and destinations to attract the right customers, while maximizing the aircraft utilization. But does your schedule management allow for maximum profitability in line with operational feasibility? Or asked differently – How do you balance punctuality vs. productivity?

Generating schedules of good quality is essential for an airline to operate in an effective and efficient way for consumer satisfaction and profit maximization. Typically airlines create their flight schedules assuming that every flight leg will depart and arrive as planned. But schedules usually turn out to be more unstable than assumed during planning due to delays and cancellations. The trend towards robust scheduling has therefore become one main objective of Schedule Management with significant results: A more robust schedule reduces the occurrence and impact of delays hence reducing costs. In this blog, I therefore present some approaches to minimize passenger disruptions and achieve robust airline schedule plans

What is a robust schedule?

Before I start to give some approaches for more robust scheduling, we should define, what a robust schedule is: A robust flight schedule is an indicative measure of how good the schedule is, because it allows the airline to cope with the unexpected disturbances which normally occur on a daily basis in a certain frequency. The important question is:

How can you build up a robust schedule in Flight Scheduling?

In the following two blogs we will discuss the following five approaches:

Create rotational buffers
Implement maintenance buffers
Eliminate unnecessary rotational buffers
Consider Crew Pairings while creating the Flight Schedule
Intensify Communications between Flight Scheduling and Crew Management during Rostering Phase.

1. Create rotational buffers

Buffers give protection between to separate consecutive legs by adding time to the minimum ground time to avoid that disturbances that normally happen on a daily basis will affect the whole system and make it less harmful. The difficult question is: How to decide about where to put the buffer and for how long? Should you do it between each leg? Are there differences for different aircraft types, airports, destinations, seasons, day of week, etc.?

The solution is quite easy: To identify the right buffers I recommend strongly the utilization of Business Intelligence tools – like data analytics or business analytics These tools shall allow you to learn from the past by comparing “what was subjacent planned (block and ground times)” against “what was actually flown”.

This comparison helps to identify deviations and changes that happen periodically or as I already said “normally” on a daily basis. The next step naturally is to find out the roots and explanations: Are these changes following any patterns or are they only spikes? If we talk about patterns, interesting questions are: Are the disturbances results due to certain weather conditions, respective airports, too short ground or block times or even maintenance issues? Two examples shall make this topic clearer:

Example 1 - Patterns in block times: You might find out, that all flights coming from the east arriving in Munich have delays. Because it affects all flights, a strong head wind might most likely be the explanation. Usually head winds tend to have a substantial impact on the block times, but there are limited options to catch up these kind of delays through flying with more speed. Therefore a block time buffer might be helpful. Regarding weather conditions it is also more than advisable to evaluate a whole year due to different behavior within summer and winter periods. You might for instance find out for your BKK flights face only two month of the year a certain delays, due to a six months lasting strong jet stream phase in winter- but is on time the rest time of the year. So adjustments for a longer block time should also be done only for these six months. The topic becomes even more complex, if certain routings are airport slot critical (Airport Slot needs then to be requested in BKK and in MUC, for different periods, which may could be difficult to get the desired slots using a smaller period)
Example 2 - Pattern in ground times: All aircraft rotations coming punctually from WAW into FRA continuing to any other airport result in an actual outbound actual delay of 5 minutes. But only in the morning. So the corrective action shall be to adjust the ground times for flights coming from WAW until noon by a buffer of five additional minutes.

Every airline will find their own airline-specific results enriched by the Scheduler’s experience with disturbances. Often appointment of Ops and Sched users are planned to discuss the biggest (ops) problem flights, where a change in the schedule have to be fulfilled. This might lead also to an identified pattern that after two minimum ground times an aircraft must be planned with e.g. 10 minutes buffer for the third ground time to keep the operational stability during the whole day.

2. Implement maintenance buffers:

Besides buffers based on airport or environmental reasons, unplanned maintenance events are also one reason for operational deviations. Here airlines have two options for solution: They either consider respective rotational buffers for unforeseen maintenance events per aircraft based on their statistics. Alternatively, they provide dry reserves by having an extra aircraft fully available for a replacement in such occasions. (“Standby Aircraft”/ “Ops Reserve”)

These were the first two approaches towards robust scheduling, we will continue with the remaining ones in the second part of this blog. Until then we are already now looking forward to hearing your feedback or sharing your ideas about how flight schedules can be made more robust.

Regards

Michael, Judith, Ensuch & Sascha

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This blog sequence is a joint publication of: