View Full Version : Visual Pattern

22nd Jan 2010, 18:38
Good eve guys,

talking about a std visual boeing 737 pattern. How can you calculate the drift angle DA on downwind with wca? How many NM im out when im starting the base turn with zero wind conditions?

Thanks folks

FCS Explorer
22nd Jan 2010, 19:10
the only thing you really need during a visual pattern is to have the rwy in sight.
for orientation i usually start with rwy-point/-3 [that where i want to turn final and be 1.000ft]. from that point 90 and again 3NM gives the base turn [~2.000ft]. from this one finaltrack/3 gives the entry for the visual.
now you have a magenta " 3-mile-box". depending how sleep deprived you are you could fly this with LNAV/VNAV. but its more fun to fly the plane by yourself.

22nd Jan 2010, 19:59
Exciting new navigation systems allow him to "build" a circuit like an artist paints a canvas. A dob of speed paint here, a light brush of altitude restriction there, a joining of waypoint dots at the beginning of the downwind leg leading to another waypoint three miles abeam the threshold and a further VOR distance and bearing waypoint just before base and a beautifully placed waypoint on long final completes the MAP picture. Picasso could never match this MAP as a thing of beauty. No need to look outside on a sunny day. Trust the MAP and TCAS says one experienced captain. . . With a quiet gasp of wonder the new pilot watches the aircraft symbol slow up quite safely as the flaps extend and in-built slow speed protection keeps disaster away - not like some macho bogans who to risk lives of passengers by stupid hand flying.

Start your Base turn at 3 times your height AGL in seconds past the landing threshold. On the map, the base of the triangle representing the aircraft should be about level with the threshold.

22nd Jan 2010, 22:33
Gulp! Is wca wind correction angle?

What ARE they teaching these youngsters now-a-days?

Yes, Captain, it IS 50k vis and n'er a hairy cloud in sight and, yes, that is the airport we want to land at - BUT my map screen has failed so we will need an ILS.......no ILS and we could be up there all day!

Gawd 'elp us. No joke, either - happened to me going into Malmo a couple of years back, but it wasn't the map screen that had failed, just an ability caption on the F/O's forehead.

22nd Jan 2010, 22:43
What ARE they teaching these youngsters now-a-days?

Yes, Captain, it IS 50k vis and n'er a hairy cloud in sight and, yes, that is the airport we want to land at - BUT my map screen has failed so we will need an ILS...

Gawd 'elp us. No joke, either - happened to me going into Malmo a couple of years back, but it wasn't the map screen that had failed, just an ability caption on the F/O's forehead.

I have to agree, to be honest if someone is flying a 737 and has to ask how to figure out how to correct for winds in a visual pattern, because they can't figure it out by looking out of the window, all is lost. :(

galaxy flyer
22nd Jan 2010, 22:53
At the opposite side of coin, watch a guy who THINKS he can fly a visual pattern, not use available electronic information, and mess it up. The approach always ends in a runway.


23rd Jan 2010, 01:37
I know GF, guess I'm just an old fart. :(

Don't get me wrong, I jumped up and cheered when I first flew an aircraft with a Flight Director, thought I'd gone to heaven when the FMS came out and I believe that the HUD is better than sex*.

* Well, almost. :p

23rd Jan 2010, 02:48
drift angle : cross wind component diveded by your ground speed in NM/min.
Cross wind component: 21 kt
GS : 180 kt ---> 3 NM/min

21 : 3 = 7

to correct the cross wind use 3 time the drift or an angle equivalent to the full crosswind ( Only at pattern speed)

23rd Jan 2010, 11:10
The distraction of mentally calculating wind correction and drift angle, and looking inside to steer a computed heading while on a short visual downwind leg is stupefying. If you can't visually hand fly a jet parallel to a long straight pavement at 1,300' AGL then you should be in another profession. :eek:

23rd Jan 2010, 12:05
you might well contemplate JF's wise counsel. JT

John Farley
23rd Jan 2010, 14:30

Let us start again.

You are obviously looking for help in flying a visual circuit. Good on you.

The trouble is the question you asked suggested you are still at the stage in your piloting experience where you need to fly a visual circuit partly by numbers. That of course is not your fault but in my view it does reflect badly on the system that trained you and put you where you are today.

A lot of PPRuNe members from the earlier generations had the benefit of excellent training which they (now) assume is the minimum that should be accepted today. They are proud of beating the high failure rate among students in the old days. In other words they have good reason for feeling that they were better than those that fell by the wayside (a group BTW that probably included many who did not have an aptitude for judging visual circuits).

But, and it is a very big but, to suggest that the comments of your elders and betters are garbage is a very bad move on your part. It is extremely rude and although I know the concept of rudeness is not in general use in society these days its use in professional circles carries with it a considerable stigma.

23rd Jan 2010, 15:29
if you are flying a 737PG with EFIS or an NG you can also use the track line and put it over the reciprocal of the runway track. Saves you the mental calculation.

Good luck.

23rd Jan 2010, 15:56
3 degrees per 5 knots of crosswind works quite well as a rule of thumb ie 10kt crosswind correct with 6 degrees. (Also useful on takeoff for a wind corrected heading bug!).

As already said, 3 times your height ie 1500' = 45 sec downwind ( + or - tail/headwind correction 1kt : 1sec). If terrain not an issue or pattern, suggest if you are an FO fly a RH pattern so you keep the R/W in your visual scan. After 45sec at F5 spd 180, Drop Gear, F15 and start a desecending turn onto final maintaining approx 7/800fpm, turn final and see what you've got. Should be pretty similar to a normal app ie 2/3 mile final. Fully configure and fly the aircraft, again 2.5degree up fully configured if on profile works well!!


23rd Jan 2010, 16:37
John - the real point here, surely, is that our dashing, noble young speedwinner must at some stage in his or her life flown a s/eng a/c around a circuit in other than 'wind down the runway'? In which case, what is different? As glueball said - possibly in the wrong job?

Incidentally, I did not read that the question was about distance downwind, guys and girls - just how far out from the runway c/line to start the base turn? All part of sim and base training?

By the way, lunav - it isn't 3 x the drift! Don't confuse the young tyro.

Not forgetting, of course, that we may be talking to a flight simmer here - no clue in the profile - in which case you HAVE to use the nav display since the cat may well be in the way of the view of the runway:)

John Farley
23rd Jan 2010, 17:39

Point taken re training in a S/E piston but whether he ever hacked it to the extent that he can do it easily now, a while later at 2.5 times the IAS is not known.

His other posts suggest he is a 737 pilot. I say he 'cos the ladies tend to be a notch above the average of us blokes - although that comment is admittedly based on mil experience only.


23rd Jan 2010, 19:54
Hi Speedwinner,

JT says Are there any rules or suggestions ?

(a) abuse of another poster will not be tolerated at all ... play the ball hard by all means if the subject matter is controversial .. but NEVER the player. In using the term "abuse", we include anything of a nasty nature... including overt sarcasm, vilification, etc., etc. ..

I'm embarrassed to be included as a PPruner. Your innocent request for some tips and advise was met with sarcasm. If I was going for an interview & assessment in a 737 simulator for the first time - I'd be having doubts about who I might have to share the flight deck with also.

We are not all the same - there are some pleasant people to fly with out there.

25th Jan 2010, 11:52
Sometimes folk get a tad critical in their responses - part of life, I'm afraid.

Nonetheless, as adults we need to be able to withstand a degree of criticism, including some which might be more constructive.

Main aim in Tech Log, though, is to avoid overt rudeness etc.

25th Jan 2010, 13:22
hello BOAC,
I understand there are two questions from the beginning:
# one is relative to cross wind correction during downwind (and I answered)
# Two is relative to downwind lenght (in NM) in zero wind cond.

Please correct me if I am wrong.
15 KT crosswind you correct downwind heading with 15 (if at 180kt gs)

Capn Bloggs
25th Jan 2010, 13:58
Arr, the visual circuit. I love 'em.

First, downwind spacing/track. Use 2nm out (737NG FCTM;)) and fly parallel by laying off the drift, as mentioned by Lunav: divide the crosswind component (calculated from ATIS or ND) by the GS in nm/min to get your drift angle.

Second, when to turn base: nil wind=45 seconds from abeam the threshold - equiv to 2nm downwind allowing for the rollrate into the base turn (If you're the effo on a left circuit, tell your skipper to call "threshold"). This will roll you out on final using 15-20 AOB at around 600-700ft AGL. I don't subscribe to the variable-timing-depending-on-height concept. The wind adjustment is 1/2 a sec per knot. So if on DW you have 10kts of tailwind, turn at 40sec.

Last, when to start final descent: if at 1500ft, descend as you commence turning base. If at 1000ft, descend half way round. If at 600ft, descend as you get onto final.

Checklists? Slats at entry, mid-Flap straight after, gear abeam the threshold, landing flap straight after then checklist. Try to finish it by the base turn so your can concentrate and enjoy yourself.

Have fun.

25th Jan 2010, 23:37
Lots of sound advice there for getting back to basics. With the modern kit you can make it ever so much easier without having to do your 3 times table as well as hand fly the beast. As JF has said us mere males aren't so good at multitasking.

If you're practising in the sim and the man in the back has kindly left you the flight path track flight path vector display, then use the map range ring to fly your downwind 3 miles abeam (assuming 1500 agl). You can nail the drift by flying a track the reciprocal of the runway track adjust in or out as you wish by using the wind vector. Timings as before, 45 seconds at 1500' agl, 30 at 1000 etc. If the wind isn't severe then not correcting for a tailwind whilst downwind will put you under the final glide slope, which is much easier to deal with than being too close and above the slope. Configure as you need but as said before, 15 - 20 degrees angle of bank with a rate of descent 700 - 800 feet per minute should see you slotted in nicely.

In our company all captains are right hand seat checked each sim by flying engine failure after takeoff, visual circuit, (normally) late missed approach, single engine go around and another visual circuit to land. Apart from all the knobs and switches being in the "wrong" place, it's normally quite relaxed and good fun. As the man said, enjoy.

26th Jan 2010, 11:04
As JF has said us mere males aren't so good at multitasking.

.. which is why the ladies are streets ahead of us mere males in a great many endeavours ... bless their little cottonsocks ...

26th Jan 2010, 12:09
Spacing: If NG put the Map range to 5nm; put the TK line // to the Rwy centre line. It's a picture and the Rwy QDM doesn't matter. To allow a slight square base leg and give room for some adjustment to the descent path before finals you need the rwy to be 1/2 way between the 1st & 2nd ring.(Does the classic have range 5nm or still 10nm as minimum?) When you've established this pick a ground feature ahead to keep on track. Be aware of tail or head winds on base leg and adjust accordingly.
If flown on the line a CDA visual circuit is preferable. Flying lowish level with drag and level flight is frowned upon.