…and when did you make your last mistake at the ticket vending machine? Error minimization strategies in Slot Management.

Source: Own photo

Slot Management is still managed at many airlines in a manual-oriented manner. But looking at our human nature, such manual working routines imply a high risk of human errors that naturally happen. Please read my blog to get some ideas how an efficient error minimization risk strategy might look like.

…and when did you make your last mistake at the ticket vending machine?

If you ask me this question, my answer will be: Just last week when going to the airport. I struggled again with the Berliner ticket vending machine that I really know for many years. What about you? When was your last time?

Well, if you continue reading my blog, you will know, whether you match the average or are below or above the error rate for the activity “wrong selection at a vending machine”.

We are human beings

Technically speaking, the “wrong selection at the vending machine” means: I made a mistake. More specifically speaking: I, as a human being, made a mistake in an everyday activity. And here we are: Every time the ‘”human factor” is involved – and this happens by default when executing manual tasks – one fact that automatically comes along with is the chance of a “human error”.

The “human error”

You, I and everyone (and of course flight schedulers / slot managers, because this is the overall topic of this blog) are humans. Human error is natural. It is the result of the human brain’s design and its limitations. We actually need to make mistakes to help us learn. Although human error is inevitable and normal, it does not mean a mistake has to end in failure.

In the airline industry a failure can result – worst case – in a big catastrophe. That is why airlines put specific focus on safety mechanisms to ensure all passengers arrive at their destinations – safe (and of course on-time)! Operational examples for error-reduction that should ideally go against zero, are the two pilot cockpit and redundant systems during flight execution as well as checklists and four-eye principle for maintenance and overhaul activities. For back-office organizations, such as the scheduling / slot management departments, with high ratios of manual tasks of course a failure does not result in being “mission critical”. But also here, human errors are inevitable and can cause at least additional costs or revenue losses. Minimization strategies should be implemented in back-office-organizations as well.

Potential errors of (manually working) flight schedulers / slot managers

Slot management represents a typical back-office process with lots of manual tasks in daily business, especially when only standard office software or office tools like e.g. Word, Excel or email are in use. For these organizations the following errors can occur, for example:

  • Use of incorrect (telex) syntax / format
  • Typos / semantic errors (wrong flight number, airport, coordinator address, etc.)
  • Doing copy and paste wrongly (e.g. you accidently cut off the last digit)
  • Identifying the incorrect coordinator answer (for the respective request)
  • Misinterpret / read telex information mistakenly
  • Transferring a response telex into the wrong file
  • Miss a cancellation (= error) that causes the loss of a grandfather slot (= failure)

About how many errors are we talking about?

There are no specific (benchmark) studies available about how many errors flight schedulers / slot managers that predominantly work on a manual base make. However, a study about error rates conducted 2005 by Dr. David Smith gives meaningful clues about the influence of the human factor.[1] In his study Dr. David Smith refers to human error rates for some exemplary tasks. These errors can be categorized with regard to complexity. There are four of them: The range is from “simplest possible task” to “complicated non routine tasks”. He also differentiates the activities into three categories: “read reason”, “physical operation” and “everyday yardstick activities”.

To get a better feeling for the error rates that we all most likely know from our personal life, I would like to refer to two “everyday yardstick activities” of his study:

  • We accidently leave three times the light on, when leaving 1.000 times the room (or apartment).
  • When buying something on a vending machine, we make 20 times a wrong selection per 1.000 selections. (Can you remember being somewhere in a foreign city and buying a metro ticket on a vending machine. Even in my own city I almost click every time at least once something wrong. That sounds very reasonable to me.)  

With the next category “physical operation” we already match specific slot management activities, such as manually typing telexes (or cut and paste a telex template and update with necessary information, such as dates, flight numbers, routings):

  • If we type or punch a character, we do ten errors per typed 1.000 characters.

Last but not least the “read error” category, which from my point of view represents similar activities executed during manual-oriented slot management working routines: Here the incident rates rise with the complexity of the task. For each 1.000 opportunities / activities we make the following mistakes: 

  • One error when reading a checklist or digital display wrongly
  • One error when checking out for a wrong indicator in an array
  • Two errors when reading single alphanumeric wrong
  • Five errors when reading an analogue indicator wrong
  • Six errors, when reading a 10-digit-number
  • 50 (!) errors when putting a 10-digits into a calculator

The last task with the comparatively high error rate represents already a routine task, “where care is needed”[2], whereas the others are “simplest possible tasks” or “simple tasks”. This explains its “error explosion”.

What is the message?

As you can see, human error rate tables confirm that the “human factor” and the “human error” is real and unavoidable. We do not perform well when tasks are structured or supported in ways that especially require great care. Therefore, when it comes to implement human error minimization strategies in slot management the paradigms must be: Standardization and simplicity.

It is clear that whatever can be done to simplify things and remove error-prone manual tasks will result for sure reductions in human failure rates – everywhere and also in manually-oriented slot management. This goal can be achieved within airlines by simply implementing and utilizing IT supported slot management systems existing on the market. Dedicated slot management and monitoring applications have the following beneficial effects, as for instance:

  • Ensuring the right telex syntax
  • Full- / semi-automatic generation of slot messages with the correct slot information
  • Correct linking of coordinator replies (like sorting the right answer to the right request)
  • Overview about open slot requests or missing coordinator answers
  • Up-to-date overview on still possible cancellations
  • Warning, if a historic slot right is in risk

Consequently, the tangible benefits of dedicated slot management and monitoring tools can prevent you from:

  • Revenue loss, because of a lost slot, or
  • Additional costs, because of penalties that have to be paid to airports for departures or arrivals outside the defined slot ranges, such operations “off slot” might end up in four to five digit worth penalties at very restrictive airports.


Human error will never be zero. Human error happens because we are human. This fact is unavoidable. Human errors can also not be stopped by wishing they simply shall not happen.

In conclusion, it became clear, we ourselves are one of the greatest remaining cause of failure. Currently, the only protection against our human error is to design and manage our business processes in that way, that we protect especially manually-oriented airline business processes, like slot management, from ourselves by implementing standardization and IT support. For slot management measurable benefits will have the following result: Avoid potential revenue loss and additional (penalty) costs.

One last personal insight...

Finally, a personal insight: While typing a text, have you ever observed how many typing mistakes you make that were automatically corrected by Microsoft Word® and you just continue typing as nothing has happened? I just have counted my typos while writing this blog. Well, I am not going to tell you my (embarrassing) error rate though J…

So what are your thoughts about this? Please feel free to share your thoughts here. You are also more than welcome to contact me for more information about this topic.


[1] Smith, Dr. David: Reliability and Maintainability and Risk. Elsevier (2005), Appendix 6.

[2] Smith, Dr. David: Reliability and Maintainability and Risk. Elsevier (2005), Appendix 6.