Why Can’t We Use That Plane?

I’d like to discuss some of the issues with changing planes.  In the following scenarios, we will presume the flight is departing from a major hub for that airline.

Have you ever been scheduled on a flight that was delayed due to a mechanical problem?  Then the gate agent announces the flight will be delayed for several hours.  Groans are heard throughout.  As you wait for the necessary repairs to be completed, someone comments they see other planes sitting around.  They are merely parked.  Why can’t one of those be used instead?  Why can’t we use that plane? 

It is a legitimate question.  Unless a plane is broken, we should be able to use it, right?  Let me first say that the airline has already began looking for swaps to the same airplane type as soon as they are aware there will be a mechanical delay.  However, in cases where the expected delay is an hour or less, an airplane swap would cause a longer delay than the repair.  Also, in cases where customers are already on board, it is normally better to stay with the original ship. 

If the delay is expected to be 90 minutes or more and another plane is available, they airline will first consider planes on the same concourse.  However, sometimes customers will need to change concourses or have the plane moved, if a tug is available.  Have you ever had a gate change shortly before your scheduled departure?  It may be due to another plane having a mechanical problem.  Sometimes 3 or 4 planes or more are swapped in order to get a plane on the same concourse (to minimize inconvenience after a mechanical) and cover the estimated delay. 

In the above situations, we are only considering the same plane type.  However, sometimes other kinds of airplanes may be available.  Perhaps you are flying on an MD88.  If so, sometimes an MD90 is available and at some airlines, the pilots are cross qualified.  That is, the pilots can fly both airplanes.  MD90s have more seats than the MD88 so no one will lose a seat.  Please know a ship downgrade is the last resort before a cancellation. 

What if you are on an MD88 but the only plane available is a 737?  In this case, different pilots are needed.  Normally, pilot crews require a couple hours from when they are contacted to when the flight will depart.  In this case, there may be an additional delay.  Also, going to a larger aircraft may require an additional flight attendant.  They also need time. 

These are just a few of the considerations for airplane swaps.  Here is other thought airlines must consider: a ship may have ground time to cover the delay but has routine maintenance scheduled that needs to be done and swapping airplanes will put it on a rotation that to where the work cannot be completed.  Airlines will tell you safety is their first priority.   

Running airline operation is very complicated and one action can cause several ripples to expand.  Whenever I look at the many gears and cogs that go together, I am always amazed at how often it works out.  Still when there is a hiccup, these are just some of the reasons why we can’t use that plane.