March 18, 2007

You just got overrestricted.

I was reading an article the other day about how the current system gets easily overloaded, yet airspace is underutilized due to the use of standard restrictions. Someone unfamiliar with the day to day workings of the NAS concluded that a simple way to increase capacity and efficiency would be to simply allow URET (and other software not yet brainstormed into reality) to allow us to separate the actual airplanes, not just use a standard restriction which is designed to miss chunks of airspace where traffic tends to be most often.

Let me back up. Each sector is designed to do certain jobs (descend planes into other sectors, sequence traffic flows, provide approach services to small airports not within approach controls, etc). Each sector is then run by one to three controllers at a time, based on traffic load. In order to successfully accomplish the mission of the sector, limits are put upon it to decrease its complexity so that safety isn't compromised. There is only so much a controller can focus on at once. Most sectors don't have more than 5 or 6 main flows. Once a sector is deemed too complex or busy, a restriction is placed on the sector that feeds traffic to the sector in distress. Many of these restrictions are in place from 6am-11pm every day to establish a standardized flow so controllers and pilots can get used to them. Certain traffic landing at certain airports are forced out of some sectors and into others, so the complexity level in the busier sectors remains manageable. While it may not be the most efficient use of airspace, it IS the most orderly and the safer way to run things. The FAA has been having a hard time grasping that concept lately, but I'll let that discussion continue elsewhere.

Allow me to refer back to my analogy of working air traffic to not getting into an accident on the Interstate. Each lane is an available altitude, with speeds independent from the other lanes around it. Often times the best way to miss other cars is simply to change lanes. However, lets say you're in the right lane driving 50 miles per hour. The cars in the lane immediately to your left are driving 60 miles per hour, and to the left of that lane the cars are driving 75 miles per hour. Up ahead, the traffic is almost stopped due to an exit. The exit leads to a congested road that can't handle the traffic, and its backing up into your lane. So you move over one lane to the left. All of a sudden, you're the slow one. The cars behind you want to keep driving 60, so they move over one lane to the left, and now everyone is driving slower than they'd like, all because of some congestion that should only be affecting the right lane.

Adding another lane of through traffic may be a solution to the problem, but the traffic in the right hand lane still will affect all the others in a negative way. Often times, busy exits will exit sooner and create a frontage type road that is separate from the main highway. This separate exit road is similar to splitting off the sectors by altitude. You may exit a little sooner than you'd like, and likewise, descend a little sooner than desired for fuel efficiency, but it eliminates the traffic backups effecting the main flow of traffic.

The air traffic controller at the lower sector can worry about all that congestion running into the major airports, and the higher sector can worry about all the fast movers up at attitude.

If the system was controlled solely on the basis of efficiency, planes would do what their on board navigational computers told them to do. This mainly includes remaining at cruise altitude for as long as possible, and then dive bombing using idle thrust into the airport. While we cannot allow straight descent directly onto final approach, we do allow pilots to descend at their discretion to meet crossing restrictions at certain points along their route. These crossing restrictions are generally at the boundary with the next sector, or at the outer edge of the approach control. As controllers, we don't care how the aircraft descend, only they are level at the altitude issued at the location specified. Often times, aircraft will remain level until the last moment, and then descend at a quite impressive rate to make the restriction. Rates of around 4000 feet per minute are not uncommon. This is ironic, because pilots are SUPPOSED to descend at a "normal rate" in order to meet a restriction. A normal rate would be the rate if we simply said "descend and maintain xxxx". This is generally 1000-1500 feet per minute for jets. However, it is become expected that pilots will hang it up at altitude and then dive it in to the restriction.

I believe that in the future this desire to use high rates of descent into airports will serve as a basis for new airspace design. There is only one problem with this. It doesn't bode well for the lower and slower aircraft that will get in the way. Imagine a sports car in the far left lane suddenly cutting across four lanes of traffic to make the exit. Ok, now imagine a bus doing it! The only way that can be safe is if there is no other traffic around, but that would defeat the goal of increasing capacity, now, wouldn't it!?

We can't make the NAS efficient for everyone all the time, but we can slightly inconvenience a few planes here and there to make sure its SAFE and ORDERLY for everyone all the time. No sense saving gas if you never make it there.


March 10, 2007

I'm Super, thanks for asking.

There has long been a rivalry of sorts among aviation enthusiasts between Boeing and Airbus. Each airplane maker has its different fundamental culture and design philosophies. These differences are too complicated to discuss here, but they encourage both those individuals who fly them, and who wish they could fly them, to argue amongst themselves over which philosophy is better. Those who fly Boeing have coined the license plate holder: "If it ain't Boeing, I ain't going." I personally prefer Boeing. Call me a traditionalist... Or American?!

Well, Airbus is almost done with their new humongous A380. If you haven't seen what it looks like, just imagine a Boeing 777 with a full length second deck. It one-ups the B747. Very ambitious, and it has promised to increase efficiency on all levels for the airlines who fly it. There have been years of delays, ranging from electrical issues to new data that shows the plane may not be as structurally sound as Airbus claims it would be. A few airlines have given up on it, and pulled their orders recently.

On a personal note, I always complain about airlines that fly 15 flights a day between two cities, with many of the flights in small aircraft (as opposed to less flights with larger aircraft) just so they can tell their customers "we fly there 15 times a day, don't worry, you'll make it there". This is one of the reasons there are so many delays. The reason this is frustrating is because there are only so many runways, and there is only so much airspace, and it seems like a waste of space. In the en-route environment, every airplane looks the same on the scope, and we always need 5 miles and 1000 feet regardless if its a B767 or a CRJ. Once closer to the airport, the approach controllers need an extra mile or two here and there for the bigger planes, but its not as much as adding another plane.

Needless to say, I really didn't have any opinion one way or the other on the new big-bus. It seemed like a good idea to me, especially if airlines would replace thier two 757s with one A380. I take that back, you'd get to replace 4 757s with one A380. Now, I'm sure thats not the plan, but I can dream of less targets out there. Its mainly going to be flown in Europe and Asia, but we'll see a few of them here and there.

With that said, Airbus is flying a publicity flight into JFK this month to show off their new bird. I got to take time out of my busy schedule to attend a briefing on the "event" a few days ago. Turns out, the A380 isn't as efficient as it would seem. Enroute still only needs 5 miles, 1000 feet. But in approach control (and when Center is sequencing to handoff to approach control), the spacing increases to 10 miles, 1000 feet for wake turbulence. Thats 3 times the spacing needed between two 737s. Thats twice the spacing needed between two 747s. And frankly, at the Center, I think we'll be cautious about putting another airplane behind it and below it, regardless of how legal the separation remains.

So, the moral of my story:
This massive plane that is like two airplanes in one, needs to be treated like two airplanes for separation. It should be a winner. Oh, wait, I almost forgot. Our current weight/wake turbulence categories of Small, Large, Heavy is getting a new classification: Super. Look it up on March 15. It'll be right there in the 7110.65. "traffic 2 oclock, 6 miles, northbound, at 12000, a super A380, caution wake turbulence". Sounds like a PR move by Airbus to me. They'll need all the help they can get.