January 20, 2010

Wobbily (or the "self vector")

This is a VOR.

While most planes that fly around these days are equipped with fancy GPS receivers, there are still a few that don't; namely, some cargo 727s and the Northwest/Delta DC-9 fleet. We also work some smaller general aviation traffic that can't afford, or have no need, to upgrade beyond VOR (ground based) navigation. In addition, many of the no-longer-up-and-coming Very Light Jets never got their GPS's IFR certified.

Aircraft with GPS can be cleared direct to any point they wish, assuming such routing is safe and orderly within the context of the NAS. In my area's case, eastbound traffic can be cleared as far as the start of the North Atlantic route structure (where Canadian controllers transition to non-radar procedures). Westbound traffic can usually get whatever they want, as long as it keeps them north of the NY-Chicago line. Southbound traffic has to go through NY Center, so they don't get anything! Aircraft without GPS are confined to airways that are connected by operational VORs on the ground or by controller provided radar vectors. It should be noted that while GPS aircraft still fly the same routes as non-GPS aircraft, overflying the same VORs and waypoints, these GPS aircraft can still use the VORs in a virtual manner even if they are out of service. There are some conflicting rules about this when aircraft are below radar coverage (MSS departures that have GPS aren't allowed to fly over MSS VOR in their initial clearance because it is not receivable below 10000 to VOR only aircraft). The rules haven't caught up with our technology. We are still forced to clear aircraft short to a local NDB, as I've mentioned in previous posts.

Since VORs are slowly being phased out, less money has been delegated to their maintenance. They have become less reliable and their signals have become less powerful.

While VORs have never been as precise a navigating tool as the GPS is currently, it has become noticeably worse in recent years. Aircraft THINK they are navigating directly to a VOR on their radial, as indicated on their instruments, but their track tells a different story.

This DC-9 was cleared direct and was receiving SYR VOR at point D in the photo above. The aircraft stays on course according to the on-board instruments. Little does the crew realize how many extra miles they are flying by not having GPS. SYR VOR has always had a nasty tendency to make aircraft "dip" to the south, and then once the aircraft gets much closer, they turn back towards the actual VOR location and fly straighter.

I prefer my planes to fly direct to the next point in their flight plan in the straightest line possible, if not just because it looks better, but also, because it is the shortest route out of my sector. That is good for everyone involved. If an aircraft files non-GPS in their flight plan, I try to help them out and keep them close to their intended route as much as possible. This does add workload and radio transmissions, so they can't always be accommodated as I would hope. Also, if a DC-9 is first in line to DTW when there is in-trail spacing...well, I don't want them adding more miles to their route of flight. Every mile that non-GPS aircraft adds to its route, I have to delay the rest of the pack behind them.

So I try to watch the DC-9 as it heads west on J547 (straight line airway between CAM and SYR). They naturally wobble a little as they recapture the outbound CAM radial, adjusting for the wind and the weakened signal. When I get a few target hits in a row that line up well with J547, I jump into action. See point A below.

"Northwest 7xxx, fly present heading, vectors for SYR, expect direct SYR when you get a little closer."

Then once they are approaching SYR (point B, below):

"Northwest 7xxx, cleared direct SYR, contact Cleveland Center 119.37, good day."

These two pictures above are tracks from the same DC-9 flight from PVD-DTW a few days apart. The difference is that I assigned present heading to the second one and didn't let them fly all over the place. Of course, if the plane will need to be vectored for spacing to DTW then I just let the SYR VOR signal do the spacing for me!

This last picture is the GPS equipped Regional Jet that was cleared direct BUF south of CAM and flies a nice straight line to get there. Yes, they got a nice direct route because they had GPS. This RJ flight flies through a completely different sector (Rockdale instead of Utica like the DC-9s above) but only because the of the late night time frame. It flies through after the busy evening traffic but before the last big eastbound rush of the night, with lots of BOS, MHT, PVD, and ISP traffic descending in that airspace. The DC-9s come through in the late afternoon, and even if they had GPS, they wouldn't necessarily get a shortcut. That just wouldn't be safe or orderly for the Rockdale sector.

Now that we've established that GPS is great and planes can go anywhere they want, the next post will discuss why planes don't always WANT to go direct to far away places, regardless of all that NextGen hype about point to point VOR navigation killing the airlines with longer routes and wasted fuel and time...

Till then...


I updated the first picture to include what "direct SYR" should have looked like (the radial, not J547, that the DC9 was following to get to SYR) with a line and arrows.

As always, thanks for flightaware.com for their tracking maps!

January 11, 2010

This is Normal

Sometimes I'm glad I just sit in a dark room and talk to airplanes over the radio because there are times when my restraint would go by the wayside and I just want to reach over and smack the pilot up-side the head, but I'd get in trouble if I did that....so.....

I'll just tell you about it.

I was sitting at Albany radar, and it was slow. Saturday evenings tend to be that way. There were a few lingering European arrivals coming into Newark, and we had 15 miles in trail that we had to give to New York Approach. The first plane calls himself Mystral zero zero three, although where Mystral comes from is nothing but a Mystery to me. Since I don't have any traffic, I just descend him to 16000 without a restriction at ALB; they'll probably cross it anyways out of habit. He is assigned Mach .81 since a Continental jet is close behind assigned Mach .78.

I ask the Mystral what his "Normal" speed would be (if you didn't have a speed assigned, how fast would you fly on your own?) He responds, "uh, we go 290 knots, but can go faster if you'd like, sir". I love polite foreign pilots. "Rgr, standby."

"Continental 55, what speed would you transition to normally?"
"Uh, we can do whatever you need, what would you like?"
"Continental 55, that wasn't what I asked, if I deleted your speed restriction, what speed will you transition (from mach number to indicated knots) to normally"

I'm a compromising kind of guy. Mystral said he'd go faster, so if COA WANTS to speed up to 310 or something, I'll give them both 300 knots. If COA is currently assigned faster than he would normally be flying, I'll just let them both fly how they'd like and the spacing will work out on its own.

"We'll do whatever you need us to do, center, Continental 55"

At this point, I just want a number. Anything. Lie to me. I don't care. Whatever, I'll just turn this guy out and get my spacing that way.

"Mystral 003 maintain two niner zero knots or greater, thank you."

Continental comes back and responds that "normal is 290 as well". "Roger, upon leaving FL230, resume normal speed." Sigh. Once below FL230, the COA55 is in my airspace and I turn him right to a 270 heading to get my 15 miles. My D-side gives me some crap about wasting transmissions and I re-clear the COA55 on course.


This has happened before. I recall a similar instance a few months back during the early morning rush at DNY/HNK sector.

We needed 20 miles in trail for LGA props, and, as always, the ROC and SYR departures were mostly tied up. I won't name names because, frankly, this is a little embarrassing. They are both Dash 8-200s (see picture above), and the first plane is flying along at about the same speed as the other, if not a few knots faster, so I plan on assigned that speed or greater to make sure he doesn't slow down without telling me. I'll vector the second one to get the 20 miles I need and then assign the same speed or less to keep the spacing. Both planes are the same type, so I'm pretty sure if the first one can fly a speed, the second one can do that too...

"callsign, you're number one to LGA today, say speed." Pilots feel special when you tell them they're first!
"Roger that, Center, we'll give you anything, what do you need?" Seriously.
My D-side and I both exchange the "answer the question without asking another question" look. My first thought is to answer his question with ultra-sarcasm, like Mach 1, or something. My second thought is how tough would it be to make this guy number 2...I tone it down a little...

"callsign, roger, maintain 290 knots or greater, advise if unable". Nothing but professionalism at all times. I know they can't go that fast (the 'advise if unable' is the hint not to accept the clearance), but you said you could give me anything I needed, buddy, and 290 knots sure would help my spacing!

"Roger, 290 or greater."
My D-side exchange another look, this one almost comical. He SOOOO didn't just take that clearance, did he!?

Then another voice, most likely the captain, keys up with a "uh, we can't do that, how about 220 knots?" That's more like it.

"Roger, maintain 220 knots or greater."


Till next time....