Divert? Stick to the Plan?

The decision to divert to an alternate airport requires a close watch on the fuel gauge.

There’s an old saying that every student pilot has heard at some point in their training: “The three most useless things to a pilot are the runway behind them, the altitude above them, and the fuel they left behind.”

Pilots love to have lots of fuel, but it’s expensive to carry excessive amounts (called “tankering” in the biz), and the company doesn’t like to spend money unnecessarily. Federal Aviation Regulations (FARs) dictate the minimum fuel loads required for a flight. For domestic operations, we must carry enough fuel to reach the destination airport, then fly to the most distant alternate airport (a suitable field selected based on weather forecasts), and then fly at normal cruise speed for another 45 minutes. (If you want to read the actual regulation for airlines, see FAR 121.639; for general aviation flights, see FAR 91.151 and FAR 91.167) In many cases, the company will pad this amount with “Contingency fuel” which is just what it sounds like, i.e., just a little extra for more options.

Fuel became an issue on one of my recent flights. We were flying from LAX to JFK, and it looked like we’d be about 20 minutes early. We were within an hour of landing and the weather looked good in New York, so it came as a surprise when New York Center gave us holding instructions. This was particularly unexpected since we were still at our cruise altitude of 39,000 feet. Most airborne holding occurs down lower, when we’re closer to the destination airport. The reason for the holding was weather on the arrival route.

The holding instructions were: “Hold northwest of the HOXIE intersection on J70, right hand turns, 20 mile legs. EFC 1850Z. Reduce speed at your discretion.” We brought the power back a little to save fuel, slowing to about 240 knots indicated airspeed — still a safe speed for our clean (no flaps) configuration. Our true airspeed (TAS) was still around 445 knots. We programmed the FMC (Flight Management Computer) for the hold, then got to work developing a plan in case we couldn’t get in to JFK. These can be some of the busiest situations in airline flying, as we have to continuously monitor the weather situation and our fuel state.

The EFC is the “Expect Further Clearance” time. This is an important part of the clearance. If we were to lose communications, we would hold until that time and then proceed according to our flight plan, knowing that ATC would clear the path for us. It also gives us an idea of how long ATC expects us to hold, but that can vary significantly either way. I’ve been released from holding before completing one turn, and other times I’ve reached the EFC time only to be given a revised, much later, EFC.

As we made the first turn at HOXIE, I made the required call to ATC to let them know we were entering the hold. Then I got on the PA to let the passengers know what was going on. I’m sure there were a lot of groans in the cabin at that point, as everyone with connections started wondering just how bad the rest of their day was going to be. We looked at several possible divert airports, and Buffalo looked like the best option based on weather reports and proximity. It was within 100 miles of the hold, which is very close when you’re at 39,000′, so things would get busy if we decided to go there. We decided on a “bingo” fuel figure, i.e. the least amount of fuel we felt comfortable with before diverting. Then we got out the charts for Buffalo.

After about three turns in the holding pattern, the controller called to revise our EFC, making it 1920Z. We could now plainly see that we would reach our minimum fuel before the EFC. This might seem to dictate making the diversion now rather than waiting — why burn fuel for no good reason? — but again, it’s not unusual to be released from the hold prior to the EFC. Just to keep ATC in the loop, we let the controller know that we would have to divert before reaching the EFC and that Buffalo was our planned diversion airport. At this point, I was pretty sure we’d be shuffling off to Buffalo to refuel and wait out the weather.

Then, as often happens, New York Approach started accepting arrivals and we were given clearance to continue on our flight plan route. We advised our dispatcher via ACARS (Aircraft Communications Addressing and Reporting System, a sort of on-board email system) that we were continuing towards JFK. This gets to be the tricky part, because we aren’t really assured of making it into JFK but now we’re getting farther from the alternate and burning more fuel. Our dispatcher calculated that we should have at least 11,000 lbs of fuel on board to divert from JFK to Buffalo with comfortable margins, and we concurred. If that did become necessary, we’d refuel at Buffalo and wait out the weather.

It looks beautiful, but you don't want to fly through it.

It was apparent as we continued to JFK that we would be going below that 11,000 pound number before landing. If it had been night with no other obvious options, we very likely would have just headed to Buffalo rather than get ourselves into a situation where our options disappeared. But in this case, it was mid-afternoon with good visibility for us and we could plainly see all of the scattered build-ups of cumulonimbus clouds. There were other suitable airports much closer to JFK (e.g. Bradley and Providence), and we could see that the weather was better to the north.

Approach control vectored us for the ILS to Runway 22L, and when it was all over, we shut down with just over 9,000 pounds of fuel — well above what would even be considered a “minimum fuel” state. (In the 757, we would declare “minimum fuel” when getting down to 4,500 lbs; we would declare “emergency fuel” at 3,500 lbs.] We were about an hour late, and it’s likely that some passengers missed their connections, but there was very little grumbling as they deplaned. Most reasonable people understand that there are factors out of our control.

As I walked off the plane, heading to the crew room, I heard one woman asking the gate agent how to get to terminal three. I volunteered to be her guide since I was heading that way. She had a connection for Moscow, scheduled for 4:10 pm. It was already after 4:00 but maybe the Moscow flight was late due to the weather. It was a long walk, but I got her to the gate and the flight was late. So I know of at least one passenger who got to where she wanted to be that night.