Operating an airline is a complicated orchestra of moving pieces when all is normal. Introduce delays, and things get exponentially more complicated. Let us take a look at some of these not-so-obvious issues.

Crew duty

We want healthy, well-rested pilots operating our flight. Fatigue and driving airplanes don’t mix well. The FAA establishes crew duty limits for pilots. The rules were changed a few years ago from what was a complicated set of regulations. The old rules have been replaced by a much more complicated set of rules. The most significant change is how a flight delay affects crew duty limits.

Previously, as long as the flight left the gate with enough time to comply with the rule, delays were just part of the operation. As an example, if the pilot’s duty day was limited to 3 more hours of duty, departing the gate for a 2-hour 30-minute flight, all was ok. Even if there was an hour delay during taxi, which put the pilots over their duty day, the flight could continue at the discretion of the pilots.

Now, the time the takeoff roll begins must be within the pilot’s duty limit. The effect is to give the pilot a time to be airborne or return to the gate and enter a rest period. The result is a loss of flexibility and pilots “timing out” more frequently.

Snowball effect

Look at a single flight with a mechanical delay. The impact is moderate. The airline will need to find replacement pilots. Finding new pilots is less complicated at a hub where crews are based. Smaller, isolated airports make the replacement task difficult or impossible.

On the other hand, bad weather and air traffic control delays can affect dozens of flights. The airline can go from needing two replacement pilots in the case above to requiring 10 or more pilots quickly. Delays finding new pilots places additional stress on the operation.

Airport Capacity

In the article entitled “Nobody Likes Delays,” we explored the runway and approach capabilities of an airport. Gate and ramp capacity play a role for each airline during weather delays. The daily schedule for each gate has multiple flights with little downtime between flights. An aircraft remaining at the gate after it’s scheduled departure time causes ripple effects. When the next flight scheduled to use that gate shows up the arriving plane will either hold out and wait for the gate to be vacant. If the delay is lengthy, an alternate gate can be used if available. Changing gates is not preferable since all the outbound passengers and bags will move to the new gate.

Now let us assume we do have a plane on the ground that needs our gate. There are two choices for the airline at this point, neither one ideal. One option is to have the pilots depart the gate with an empty aircraft and reposition it to a ramp somewhere temporarily. This option is not a great one since the plane will need to be repositioned back to the gate to pick up its passengers at some point.

The next option is to load up the passengers and bags for the outbound flight. The plane then pushes back and waits at a remote location for it’s assigned takeoff time. This method has advantages and disadvantages. On the positive side, the plane and passengers are close to the runway and ready to go.

We don’t want to sit around on the taxiway.

A negative to this is something we call flight time. Remember earlier, when we talked about crew duty rules? Pilots have limits for both flight time and duty time. Duty time is what you would imagine. It is the time starting when the pilots show up at the airport for work. It continues until they leave the airport at the end of the day. Duty time consists of time in the air as well as time planning the flight and even breaks between flights.
The FAA defines flight time beginning as the time the plane starts to move for flight. Usually, pushing back from the gate starts flight time. Flight time comes to an end when the aircraft parks at the gate following a flight. Taxi time is part of flight time, even with the engines shut down. The effect is when we pushback and take a delay getting airborne it counts against allowed flight time for the day. Adding unplanned flight time is not desirable.

The big fine is not fun.

The FAA enforces a rule commonly referred to as the tarmac delay rule. The regulation is complicated and has several requirements. All we need to understand is tarmac delay applies to both departing and arriving. The airline must do everything in its power not to exceed the allowed time limits. (weather conditions, safety, and other considerations affect the decision to impose fines) The fines for these delays can be huge. Overall the rule is a good idea, but it can complicate the delay issues.
Let us look at an example. Operating a flight from Atlanta to New York, Atlanta airport is affected by thunderstorms. All departures shut down, and we sit with engines shout down on a taxiway. After a long delay, we slowly make our way up through the line of planes waiting to take off. Two and a half hours after we left the gate, we are getting closer to number one for departure. We cannot be sure of getting airborne by the three-hour time limit. We must return to the gate and allow passengers to deplane. While we may have been 30 minutes or less from take off, we could not take that chance. The penalty if we fail, is just too big. A situation such as this will probably increase our delay by at least an hour.

All these complications are, well pretty darn complicated. As a passenger, it is difficult or impossible to see all the moving pieces. Yes, there are many more moving pieces than those we discussed here. I hope this generates some understanding (or maybe more confusion?) the next time you face flight delays.

The big secret…shhhh.

I have one last secret to share. Before you take out your delay frustration on the crew, did you know the crew may be upset about the delay too? Pilots and flight attendants get paid beginning when the plane pushes back. If there is a two-hour delay sitting at the gate, the crew is not getting paid. They may even be losing pay as the delay can affect their future flight legality. Situations like these are an excellent time to break out the golden rule.

Nobody likes weather delays when flying. Passengers hate them, the crew hates them. The airline hates them.

Some delays are pretty straight forward and obvious. A mechanical delay is pretty easy to understand. If the flux capacitor breaks, we need a new one before we start our flight. If a flight attendant gets injured, we need to get a replacement before leaving. (yes the FAA mandates a minimum number of flight attendants for flight)

Air traffic control delays come in two primary flavors. Traffic congestion and saturation resemble rush hour on a big city freeway. The road can only handle so many cars at one time. An airliner cannot just stop like a car, so air traffic control has to manage the number of “planes on the road.” An en-route delay involves managing the “planes on the road” situation. Airports can handle a certain number of arrival aircraft per hour. The maximum number of arrivals per hour relies on everything working. Everything, in this case, refers to things like runways, approach systems, and radar. Weather also plays a role in the number of arrivals handled in an hour. When the weather gets worse, and runways shut down the number of flights allowed in decreases.

The weather delay can be puzzling. Watching the snow pile up on your airplane makes the weather delay easy to understand. Your ride at the destination telling you about the massive hail falling also makes things clear. But your airplane is sitting in the sunshine. Your ride at the other end is lounging on the beach. How can there be a weather delay? What weather? Where? Sometimes the weather is between where you are and where you want to be. Why can’t we fly around the weather? Sometimes, the lines of weather are long. A flight from Chicago to Denver may go as far south as San Antonio to get around the weather. This is going to be a much longer flight than planned. It may be better to wait an hour for the weather to pass Chicago than to add hours to the trip.

What about when the area of bad weather is smaller? When this happens, air traffic control comes back into the picture. Let’s look at why.

Airplane freeways.

Airliners fly in controlled airspace. Many assume the pilot takes off and heads directly to the destination. In reality, the route flown consists of airways and navigational fixes. Air traffic control manages the traffic on these airways and between the fixes. The picture above shows high altitude airways in the northeast part of the United States. You can think of these airways as interstate highways for airplanes. The different altitudes provide “lanes” on these freeways. Let’s forget your mental picture of Interstate 80 near Casey, Iowa. Replace it with a mental image of Interstate 10 near downtown Los Angeles. Let’s make that on a Monday at 5:10pm. Yes, those airways are busy.

The picture above is a snapshot of air traffic over[opik;m. the United States. This is a Monday morning around 9am.

Back to our weather delay.

You are sitting in the terminal at Boston Logan Airport so ready for your spring break trip to Miami.

It is a bright sunny afternoon even if it is cold in Boston. Your friends arrived in Miami yesterday.

They text you a few minutes ago sending pictures of themselves on the sunny South Beach. You are jealous of them when you hear the announcement your flight is now delayed 3 hours for the weather. What’s happening?

There is a large area of strong thunderstorms over the Carolinas and Georgia. The weather moves in, and the storms grow. Air traffic control moves flights to airways clear of the storms. The storms shut down airway after airway. Think back to the picture of Interstate 10 downtown Los Angeles at rush hour. A colossal accident (in our case a thunderstorm) closes Interstate 10. Cars try to switch to the 91 freeway. It doesn’t take long before that gridlocks.

Ground stop

In air traffic control world, it is time for a technique called a ground stop. The ground stop can be for a destination airport or for an en-route region. In this case, it is for the en-route region of the southeast United States. Flights are still going to our destination of Miami. They are coming from places like San Juan and Houston not affected by the en-route storms. The ground stop is a big time out. Air traffic control is saying no one takes off if the flight plan goes through the area of bad weather. Airline dispatchers are busy trying to get your flight routed around the weather. The answer to the reroute will be no if air traffic control cannot handle the flight on the new route. This is often due to traffic demands.

When issuing a ground stop air traffic control provides an update time. Usually, the update time is one hour after the ground stop begins. This update time does not mean your flight will be able to go at the update time. The time puts the pilots and airlines on hold. It keeps them from pestering the air traffic controllers every 2 minutes. (picture kids asking mom and dad, “can we go?” “can we go yet?” “how about now?”) When the update time arrives, air traffic control looks at the situation. If weather and traffic still look bad, the controllers issue a new update time. (most likely another hour from now) One trick with the ground stop, it can end with no warning before the update time. This can cause your flight to board and depart in a hurry. This is why you should stay pretty close to the gate during a ground stop. Keep reading, the fun is only beginning.

Gentlemen (and ladies) start your engines.

When the ground stop ends, the fun begins. Air traffic control can release your flight immediately. This can cause a scramble to get ahead of other flights and be front of the line to depart as mentioned above. Another option is a more measured response. The proclamation to leave You may hear a pilot mention an “edict.” They are not referring to a proclamation. They are talking about an EDCT or expect departure clearance time. This is sometimes referred to as a “wheels up” time. It can follow a ground stop or almost any air traffic control delay. The term “wheels-up time” is a good description because an EDCT requires that you be lifting off at that time. If you are still at the gate or taxiing out during your EDCT, you have “missed your time.” This can cause anywhere from a short to very long additional delay. Pilots hate to miss an EDCT time as it will delay the passengers further. Once the flight receives an EDCT, the pilots will determine a time to push back from the gate. This will allow them to taxi and perform preflight checks in enough time to comply with the EDCT. Don’t make the mistake of thinking “they won’t leave without me” once this new push back time is announced.

Hopefully, this offers a little peek inside the flight delay situation. As complex as this sounds, it is only the beginning. If your head has not exploded already read Ask The Captain Many Moving Pieces. The article provides another look behind the scenes. It discusses reasons and decisions affecting flight delays. Had a delay you don’t understand? Feel free to comment below.

Who likes turbulence?  Thrill-seeking roller coaster riders?  For the most part, as occupants of an airliner, we are not in love with it.  So back to the question of turbulence, how bad is it?

What is turbulence?

We all know what makes turbulence.  It’s the ‘air pockets.’  Conversations about pockets should probably be left to jean pockets and shirt pockets.  Let’s see if we can work in a little physics talk.  (doesn’t that sound easier than fluid dynamics?)  To all my physicist friends, engineers, and of course Sheldon and Leonard, I apologize for any oversimplification and loose language.

Is air the same as water?

Whoa, wait, you say.  Air is not water.  If we walk through the air to the sandy beach, we are dry, but if our path takes us through the water, we are going to need a towel.

But air and water do have something in common.  Air and water are both fluids.  Yes, gasses and liquids are both fluids.  Ok, we can buy into that, but why is my airplane bumping through the sky?

When fluid travels, the ride can be smooth or bumpy.  If we look at a river moving oh so slowly over a flat bottom, we see a beautiful smooth surface.  Now let’s speed that river up.  Look at the shorelines.  Can you see eddies and, dare we say it, turbulence?  That fast-,moving fluid is going past something moving at a different speed, like the shore at a speed of zero, experiences friction and turbulence.

Now just for fun let’s speed that river up now and throw a bunch of boulders on the bottom.  The picture above will paint the result.  Now when my river of air flows over mountains, it will often create rapids in the air.  So is the Captain saying turbulence is often a white water rafting ride in the air?  Yes I am.

But those air pockets have to be real right?  Well, the closest we get to air pockets is the turbulence generated by the sun shining on hot, bright sunny days.  When the sun heats the ground, the warm air produced rises.  Different areas heat more than others.  Take a barefoot walk across the white pool deck in Phoenix in July.  Now continue that barefoot walk out into the blacktop parking lot.  It is going to be a very different walk in the parking lot.  The air above the parking lot is rising faster than the air above the pool deck.  Remember our river running past the shoreline in the river?  This rising air is going to produce the same result, only vertically instead of horizontally.  Want to see this rising air for yourself?  Just watch a thunderstorm cloud building.  You can see the cloud getting taller and taller right before your eyes.  The air in that cloud is rising very rapidly.

The Jet Stream is indeed a river of air, and it can have a significant influence on the weather and turbulence.

Are you still skeptical about these “rivers of air” moving in the sky?  Watching the Weather Channel will introduce you to the strongest and often most important river of air.  The Jet Stream is indeed a river of air, and it can have a significant influence on the weather and turbulence.

What are you feeling?

Now that we know what the turbulence is and how it forms, we have to ask, who cares?  Does it matter what caused this bumpy ride?  The answer is yes.  A big part of the discomfort passengers feel from turbulence is due to facing an unknown.  Now that we know about turbulence, it is no longer a problem, right?  Well, not so fast.

The effects of turbulence

Surely this turbulence can’t be good for the airplane.  If that’s what is going through your mind, you are probably wrong.  Except for very rare very strong turbulence encounters the aircraft is pretty unfazed by this bumpy ride.  The wings have been designed and tested to handle the worst turbulence.  Taking the Boeing 787 as an example, the wings flex in flight as lift is produced.  For the 787 this amounts to about 10 feet of movement at the wingtip.  Boeing then calculates the worst expected force (turbulence) the wing could encounter.  They are required to test the wing to at least 150% of this worst-case scenario.  During testing 787 Boeing bent the wingtips approximately 26 feet.  I am talking about really bending the wing on a real airplane, not some computer analysis.  

The boxes in the back, the pilots in the front, and the airplane are not bothered by turbulence.

If the turbulence doesn’t negatively affect the airplane, it must be a problem for the pilots.  Also, not true.  If I put my coffee in a cup with a lid, it is spill-proof, and I am good to go.  My friends who fly for the cargo carriers don’t even worry about trying to get away from normal turbulence.  The boxes in the back, the pilots in the front, and the airplane are not bothered by turbulence.

The turbulence must be a problem for someone.  It is.  The flight attendants have to work harder in an airplane that is moving.  Sometimes this makes service slower, or the service gets suspended.  We know passengers don’t enjoy turbulence.  A nice full cup of hot coffee is no fun on a moving tray table.  Trying to work on a laptop which is jumping around is going to wreck your productivity.  

Turbulence restricts your ability to get up and move around the cabin, and as it intensifies, it also restricts the flight attendants.  Strong enough turbulence can be responsible for injuries and illness.

What is being done about turbulence?

We know there is no way to get rid of turbulence.  Our efforts focus on avoidance and preparation.  

Over the 30 plus years I have been flying for airlines, the forecasting products have significantly improved.  Most of this is thanks to technology advances.  Having this knowledge, I can take measures to avoid known or forecast turbulence.  At times, my flight is preplanned by dispatchers to avoid areas of known or probable turbulence.  

Even with superior forecasting, it is impossible to predict all turbulence.  At times turbulence is so widespread there is no way to go from departure to destination without experiencing some turbulence.  Having an accurate picture of turbulence helps me minimize my encounters and prepare both passengers and flight attendants for what lies ahead.

What kind of passenger are you?  Do you hate turbulence or tolerate it?  Are you one of the lucky ones who can sleep through the bumps?

Comment below and let me know.