Difference between PAR and ASR approaches
#21
#22
Gets Weekends Off
Joined APC: Jul 2007
Position: 744 CA
Posts: 4,772
When I flew C-130's in the AF....86-91.... our mins where 200 and 1/2 as directed by the MAJCOM. Nothing sweeter than the sound of a GREAT PAR controller doing his thing especially on a dark stormy night....say going into Lajes.
#23
Gets Weekends Off
Joined APC: Dec 2007
Position: retired
Posts: 992
I used to love doing PARs in the middle of the night, in a Cessna 150, under the hood, with a safety pilot, at an AFB with an F-105 Wing. You could get as low as you wanted and as long as your wheels didn't touch the runway, it was allowed. Invariably, when they found that your approach speed was less than 200 knots, they put on a student controller , but one night I remember this from a veteran controller......
"Approaching the glide path...perform your in cockpit check....your landing gear should be down and welded....on course....begin descent......"The Graduate" is playing at the base flick....on course, on glide path.....show times are every two hours, beginning at 1600 hours......on course, on glide path......they're offering two for one at the "O" Cub during happy hour......on course, on glide path........make sure your engine is running, Sir, I think you may have stopped.......on course, on glide path"
"Approaching the glide path...perform your in cockpit check....your landing gear should be down and welded....on course....begin descent......"The Graduate" is playing at the base flick....on course, on glide path.....show times are every two hours, beginning at 1600 hours......on course, on glide path......they're offering two for one at the "O" Cub during happy hour......on course, on glide path........make sure your engine is running, Sir, I think you may have stopped.......on course, on glide path"
#24
Gets Weekends Off
Joined APC: Nov 2008
Position: UnemploymentJet
Posts: 313
Yep. 1991 at Diego Garcia. No precision approach there, so the AF brought in a mobile PAR that we had been using. One night in heavy rain, one of our BUFFs ran off the slick coral runway and shut the runway down. We still had 3 or 4 jets airborne. The parallel taxiway was the old runway. The PAR guys re-calibrated the PAR for the taxiway in record time and brought the rest of the jets in on the taxiway. Those PAR guys were heroes that night. I think they all got well deserved medals for saving the day (night)!
#25
Yep, the PAR is still alive and well. On reserve duty, I shot a PAR into Missawa and Atsugi yesterday. Weather was down near mins in Missawa and their G/S on the ILS was down. I'm glad we still practice those old PAR's. It saved the day yesterday. The Japaneese Final Controller did an awesome job (way better than the American guys back home). Then we dropped off our pax, got a quick drink for the plane, and headed to Atsugi. We got another PAR to keep up the skill set we have lost in our airline gig..... this time the controller was slow, couldn't correct for the crosswind; we could see on the moving map that he was keeping us right of course. We broke out with plenty of time to correct and land. Let's hope he's not working when the wx is at mins, and the nearest island is an hour and a half away at the next 3rd world hole.
-Aloha
-Aloha
Last edited by Aloha; 05-26-2010 at 10:25 PM.
#26
More Details
ATC radars sweep 360 degrees in 6 seconds (10 rpm). This means the accuracy of what he sees on the scope is only updated once every 6 seconds. Additonally, all radars (even fancy phased-array) have something called radar-resolution cell. Without going geeky-technical, it is the size of a box your airplane can be in, and still show up at the same place on his scope. This is a physical function of electromagnetic waves, not the type of radar producing them. The size of the cell is dependent on operating frequency. For approach control radars (which are normally low-frequency), this would be a box about 300 ft x 300 ft x 300 ft; maybe even as big as 400 ft cubed.
Stated another way: the size of your radar-blob on his scope is 3-400 ft square.
Because of the time delay, and the inaccuracy of the radar res-cell, accuracy of ASR's is about the same as a VOR or TACAN: plus or minus a quarter mile at the MAP.
PAR: two separate radar units, one that sweeps side to side (not sure of the azimuth, but maybe 10 degrees of runway centerline), and one that sweeps up and down. Both of them sweep about once a second; and being higher frequency, the radar res-cell is much smaller, I think less than 100 ft laterally, and 20 feet vertically. Because the time delay is almost nil, and the cells are smaller, accuracy on final is significantly better...like flying an ILS.
It takes a lot of maintenance money to keep two radars working properly, and it takes skill on the part of the controller to do the approach well, too. That is why they are slowly going away. Not sure, but I think the Navy keeps them at training bases becuase they still use PARs on the boat. Any Navy support on this one?
The formula for VVI on final (3-degree glidepath) is one-half your groundspeed x 10. example: 160 kts; 800fpm. 60 kts; 300 fpm.
#27
You just brought tears to this former B-52 EWO's eyes with that simple explanation.
On a side note, the controllers have a lot to do with it. San Antonio eliminated their ASR capability before the T-37s left Randolph, Laughlin got rid of their capability because it was too hard to keep people trained. A poor excuse at a UPT/AETC base IMHO. Ironically now they have the new digital signal processors in the RAPCON/TRACON airport survelliance radars and their accuracy would probably go up.
Got an ASR at Waco in the last six months and the controller never got us more than 1/4 mile off the extended centerline I had drawn on the GPS moving map. I asked if he had the new radar and he said no, still doing it old school on the analogue scope. That guy was obviously an old hand at giving ASRs
On a side note, the controllers have a lot to do with it. San Antonio eliminated their ASR capability before the T-37s left Randolph, Laughlin got rid of their capability because it was too hard to keep people trained. A poor excuse at a UPT/AETC base IMHO. Ironically now they have the new digital signal processors in the RAPCON/TRACON airport survelliance radars and their accuracy would probably go up.
Got an ASR at Waco in the last six months and the controller never got us more than 1/4 mile off the extended centerline I had drawn on the GPS moving map. I asked if he had the new radar and he said no, still doing it old school on the analogue scope. That guy was obviously an old hand at giving ASRs
#28
PARs and other Trivia
Agreed about the controllers. The absolute best controllers I ever saw were while stationed in Europe. The Brits and the Germans could literally tell if you were 10 feet above/below glidepath.
#29
New Hire
Joined APC: Oct 2010
Posts: 4
Does anyone have any experience circling from an ASR? I could potentially be doing one in the near future as part of a checkride. Wondering if the controller lets you know when you are within the circling radius. Has anyone ever circled from an ASR?
#30
Once you have the field in sight call it. The controller should then announce where you are. If once you call the field, the controller responds with a distance outside of your circling radius just ask for a callout at your circling radius. It shouldn't be a problem.
Also, just because you are shooting an ASR don't neglect to tune up useful navaids if able. That colocated VORTAC, although not used on the approach, can be useful and I would have no problem if my student used a GPS to determine distance to the threshold if it was "working." Our SOP calls for the student to have a backup approach up. This approach can point you to the useful stuff to tune up.
I hope this helps.