When to descend while on a visual approach...?

[FlyKingfisher]

Hello everyone. I'm new to this forum, so please excuse any mistakes or non-compliances.

I am not a professional pilot, but am very interested in aviation. I am a simmer and I sim a lot on MS FS2004. My dilemma while flying on MSFS is 'when to descend'... In any case, I always wanted to know when a pilot decides to descend while on a visual approach.

Supposing, eg, you are cleared for a visual approach to a runway at 2000 ft, when do you start your descent and at what rate? I know MSFS has its limitations, but I would appreciate if a professional pilot can answer my question.

Do you manually make the aircraft descend using the control yoke/sidestick or do you set a minimum altitude and then a rate of descent on the V/S? I know that the rate of descent must not exceed 1000 fpm, it should be around 600-800 fpm...

[carbheatout]

start from 3,500ft (generally always 1,500ft above aerodrome level, terrain permitting).

When going downwind. 20 seconds after passing the throshold of the landing runway select gear down and intermediate flap. 45 seconds after passing the throshold runway start your turn onto final approach. As you pass throgh 45 degrees (of the 180 degree) of turn required to line up with the runway, you should become visual with the runway. At this point start a gentle 300-400fpm rate of descent and select landing flap. When fully configured with landing flap go down at a rate that is half your groundspeed. So for example if you ar 160 knots go down at 800FPM. If you are 140 knots go down at 700fpm.

[Nubboy]

It all depends............

Light aircooled piston aircraft, singles or twins, need careful handlinling if you want to preserve engine life. Going from cruise power (or even worse) climb power to idle without giving the engine a chance to cool properley will result in cracked cylinder heads. Liquid cooled engines don't have the same problems.
Thje descent technique is to work out a power setting that will give you a modest rate of descent, and keep the engine warm. Normally this will be under 1000 feet per minute. Therefore work out how much TIME you need to descend either to circuit or platform height and go down accordingly.

Turbine powered aircraft are a different matter. Flight idle is available and can be used as required. Your limitations tend to be passenger comfort. Either rate of descent in un pressurised aircaft (eg Shorts 360, Cessna Caravan etc) or body angle for draggy jets (eg F100) or accelerating through Vmo or Mmo for slippery jets (most of them).

Thrust idle will give between 1500 and 3000 fpm, depending on weight, altitude and temperature. If we let the aircraft accelerate then 6000 fpm is possible for short periods.

We don't normally fly circuits so we tend to allow 3 nm per thousand feet, plus 1 nm for each 10 kts to loose. eg from 35000 and 270 kts indicated, you need 35 x 3 plus 27 - 18 gives 105 + 9 is about 124 miles out if you want to be stable at 180 kts on the approach. Head or tail winds need factoring by about 1 nm per 10 kts.

All very rough, but it'll put you in the right area for almost any aircraft type.

[welliewanger]

Nubboy's right, I'll just add these rules of thumb.

- Height should be 1/3 of distance to touchdown (at 12 miles, you want to be at 4000' (ish)

- Rate of descent should be 5 * ground speed. So at 100kts, you need 500 ft / min

Nubboy's point about slowing down is very important too! The numbers I've just given are for if you're already slowed and configured. If you're coming down from very high (we go up to FL510) I use the same numbers and add 10NM to slow down.

[FlyKingfisher]

Thanks to all for replying. I should have been more specific while asking my question about which aircraft I'm flying and the flight rules, also I was referring to the final approach phase and a straight-in approach.

As I said, I'm not a pro, so all that computation as suggested by Nubboy is a little bit complicated for me.

"Rate of descent should be 5 * ground speed. So at 100kts, you need 500 ft / min" - I'll keep that in mind.

I'm currently flying the A320, so all my flights are IFR. To get an idea of what I should do on a visual approach, what I would do is, observe the rate of descent while flying an ILS approach, which is usually about 600 fpm. I've seen that the aircraft starts descending approximately 6-7 miles from touchdown after intercepting the glideslope. What I do on a visual approach is, when I am 6-7 miles from touchdown, I switch off the autopilot and then put the aircraft into a descent manually with flaps at 3 and landing gear down with speed at VAPP (as computed by the FMGC), then at 1,000 ft radio altitude, I select full flaps and make adjustments to line up with the runway. I've been able to land successfully on several occasions, but I sometimes have difficulty controlling the speed. I've come to realise, that I'm probably too fast when I'm cleared for the approach, the approach then becomes unstable and I have to abort and go-around.

I'm somehow not able to accomplish a smooth touchdown while flying manually. Do pilots encounter such a problem in real life too?

Also, there is a bit of confusion in my mind about the difference between VAPP and VREF. Since VREF is the 'approach reference speed' and VAPP is the 'target approach speed', do I maintain VAPP or VREF on final approach? Do I have to achieve VREF on short finals or when stabilising the aircraft at 1,000 ft as required on an ILS approach? Do I touchdown at VAPP or VREF? The FMGC on the A320 only gives two speeds VAPP and VLS (minimum selectable speed).

[welliewanger]

I'm not familiar with what's known as "airboos logique" so I don't know the strict definition of Vapp and Vls, however I do know what Vref is as it's a universal term. Here's my definitions (not gospel)

Vref: 1.3 * stall speed. This is the absolute minimum speed for the approach.

Vapp: Vref + a bit extra, e.g. for gusty winds or if there's a potential for windshear. This adds an extra margin.

Vls: Lowest selectable speed. The automatics won't allow you to select a lower speed.

The approach technique you're using is a bit advanced for someone without much training. I'd suggest getting it all configured before intercepting the glideslope (at 2-3000 feet). Configuration changes at 1000 feet will destabilize the aircraft at the last minute and not give you much time to fix it.

As for the landing... again, I'm not a bus driver but the technique is pretty much the same for all large aircraft.
50 ft: close throttles
30 ft: wait a second
20 ft: raise the nose a couple of degrees
hold it there. Don't try to land the plane. You're just arresting the rate of descent. As it slows down you'll gently sink onto the runway.
10 ft: squeeze (don't kick) off the drift with the rudder
squeek go the tyres
remember the nose is still flying. Put it down gently.

[FlyKingfisher]

The FMGC that I use on my A320 does allow VLS to be selected. I read a thread on this form (http://www.pprune.org/archive/index.php/t-165372.html) which says the following: "The VLS is the slowest speed the Airbus lets you fly. The automatics in the normal life prevent flying below this speed, but you still can dial in a lower speed than that on the FCU." :confused:

The aircraft must be stabilised by 500 ft when on a visual approach, but I find it difficult to do so (sometimes). I make my adjustments to line up with the runway well before 500 ft or even 1,000 ft (depending on which altitude I've been cleared for the approach - usually between 4,000 and 2,000 ft AGL and between 6/7 miles to 15/20 miles from touchdown).

You say: "The approach technique you're using is a bit advanced for someone without much training." What exactly do you mean by that? Am I going in the right direction?

This might seem wierd but, when I try to flare the aircraft manually after closing the throttles at 20 ft, the aircraft begins to climb away from the runway rather than settling down! :( I then have to go-around only if I don't stall in the meantime and crash.

I have some trouble controlling the aircraft during a crosswind, because I only have a joystick and no rudder pedals for yaw control in MSFS :* and it is very inconvenient to use keys to control the rudder. What I've done now is adjusted the joystick so that it gives me both roll and yaw. The aircraft handles better now.

[welliewanger]

My comment about advanced technique referred to configuring late in the approach. As you take flap, the aerodynamics change significantly. Try getting the gear and flaps out sooner so that you can be all stable and configured well in advance. Only when you've got this all nailed should you move on to configuring late.

It sounds like you're overdoing the flare. It's only a few extra degrees nose up. Take a look at some youtube videos and you'll see.

Crosswind landings require you to put crossed controls in (wind from left requires right rudder and left aileron) so having the joystick do both won't work all that well (unless you've got a joystick you can twist)

[FlyKingfisher]

My comment about advanced technique referred to configuring late in the approach. As you take flap, the aerodynamics change significantly. Try getting the gear and flaps out sooner so that you can be all stable and configured well in advance. Only when you've got this all nailed should you move on to configuring late.

I just realised that even while being vectored for an approach, I was too fast - 200-250 KIAS. It's only when I saw an approach chart did I realise it. I now reduce my speed to 180 KIAS when I'm about 30 miles from the airport with flaps at 2. In real life, speed at 200-250 KIAS within a 30 mile radius of an airport you're about to land into, would probably be a gross mistake. Am I right?

It sounds like you're overdoing the flare. It's only a few extra degrees nose up. Take a look at some youtube videos and you'll see.


I probably am, but the joystick controls are too sensitive... a small movement on the stick results in a large movement of the aircraft. So, I've stopped flaring the aircraft manually. I've seen that at the correct approach speed, the aircraft flares itself (again I don't know if this happens in a real aircraft). I select a speed lower than VAPP, eg, if the FMGC has computed 138 KIAS I select 130 on the FCU. Would that be a right thing to do? It works well though.

Crosswind landings require you to put crossed controls in (wind from left requires right rudder and left aileron) so having the joystick do both won't work all that well (unless you've got a joystick you can twist)


I realise that... My joystick doesn't twist. MS Flight Simulator has its limitations :(

[computer jockey]

Visual landings do take practice, especially in MSFS where you do not have all the visual cues you would get in real life.
I would suggest you practice at a larger airport where you have the PAPI lights available (the horizontal line of red/white lights next to the runway). Make sure you have visual on the runway and are lined up nice and early. Good advice from welliewanger to get your configuration set up while you are still in straight and level flight, that way you don't have to worry about adjusting trim etc when you deploy flaps and gear.
As you approach the runway, you will see 4 white lights on the PAPI, then 1 red and 3 whites, then 2 reds and 2 whites. This is the time to start your descent. Gently tilt the nose down and check your speed. The speed will increase as you go "down the slope", so reduce throttle. Try and keep 2 red and 2 white lights until you reach the threshold. 4 whites mean you are too high above the glideslope and 4 reds mean you are too low. Use gentle inputs of throttle and elevator to keep you on the slope.
After a few of these, you will recognise automatically when you are too high or too low from the shape the runway makes ahead of you.
You are right that 250kts is too fast. Slow down well ahead, 180kts would probably be right. If your speed is too high on when you flare, you will climb again as you already found out.

Finally, invest in a good joystick with twist control. I recommend the Logitech Extreme 3D Pro which I have had for many years. You need to have separate axes for rudder and ailerons when you try cross wind landings. Also, get the paid version of FSUIPC by Peter Dowson (from AVSim etc.). This will allow you to adjust the sensitivity of your joystick.

Happy landings!

[ZOOKER]

When you are visual with the landing runway and surrounding terrain and no doubt exists that continuous visual reference to these features can be maintained until touchdown. :ok:

[NudgingSteel]

A rough rule of thumb is that, for a 'normal' 3 degree glideslope, your rate of descent (in fpm) should be five times your groundspeed (in knots). Therefore if you're doing 150kts then your rate of descent should be 5*150 = 750 feet per minute.

For a 3 degree glidepath, you should descend 300 feet per mile. Therefore at 10 miles from touchdown you should be at 3000'. 5 miles out you should be 1500'.

PAPIs should be set to assist this - look for two red and two white. Four whites means you're too high. Four reds means too low. In the immortal words of David Gunson, four greens means you're seriously low as you're looking through the grass at them!!!!!!!!!!!!

[ZOOKER]

Steely,
Not quite correct.
PAPIs were not common when that speech was recorded.
David actually referred to their predecessors, called VASI, - Visual Approach Slope Indicators. I believe he described them as "an Ovaltine tin, with a plate welded in at 3 degrees".
Sorry if this sounds a bit pedantic, but to quote 'The Goodies'. -
"GET IT RIGHT".

[Coffin Corner]

Forget trying to work out 5 x Groundspeed for your rate of descent, just work out ½ groundspeed. It is exactly the same figure, for instance:

Groundspeed = 140kts

5 x 140kts = 700fpm descent rate

½ of 140kts = 700fpm descent rate (ok I know it's 70, but it's an easier calculation)

CC

[FlyKingfisher]

Visual landings do take practice, especially in MSFS where you do not have all the visual cues you would get in real life.

Quite right. It's like those F1 racing games where it's difficult to control the car. Much easier in real life. I reckon it must be a lot easier to line up with the runway in a real aircraft just like it's easier to drive a real car. Lot of cues missing in MSFS.

When you are visual with the landing runway and surrounding terrain and no doubt exists that continuous visual reference to these features can be maintained until touchdown.

My question should have been: When do I initiate decent once the runway is in sight? Sorry for not being clear.

A rough rule of thumb is that, for a 'normal' 3 degree glideslope, your rate of descent (in fpm) should be five times your groundspeed (in knots). Therefore if you're doing 150kts then your rate of descent should be 5*150 = 750 feet per minute.

For a 3 degree glidepath, you should descend 300 feet per mile. Therefore at 10 miles from touchdown you should be at 3000'. 5 miles out you should be 1500'.

PAPIs should be set to assist this - look for two red and two white. Four whites means you're too high. Four reds means too low. In the immortal words of David Gunson, four greens means you're seriously low as you're looking through the grass at them!!!!!!!!!!!!

I'll pay more attention to PAPI/VASI.

Forget trying to work out 5 x Groundspeed for your rate of descent, just work out ½ groundspeed. It is exactly the same figure, for instance:

Groundspeed = 140kts

5 x 140kts = 700fpm descent rate

½ of 140kts = 700fpm descent rate (ok I know it's 70, but it's an easier calculation)

CC

A lot easier! Thanks. :)

[Wabid Lithper]

Will depend on airspace arrangements, (I believe) local/jurisdiction procedures as well as flight category.

[One9iner]

tune in the ILS frequency and hit APR!

[FlyKingfisher]

tune in the ILS frequency and hit APR!

Oh! How very simple :) After so many years of keeping in touch with flight deck technology, how come I never thought about that :ugh:

[Gentle Climb]

I had a go on MSFS a couple of weeks ago and the A320 did seem far trickier to land than the 737-800. It might be due to me having a better idea about the -400 but the control seemed vague at best.
Regarding speeds...slow down! by 25nm get 210 clean, 20nm get 190 flap 1, 15nm 170 flap5. It doesnt take long to travel...you are doing more than 3 miles a minute. Descend using PAPI or roughly 3 miles for every 1000agl.
Make sure speed is under control, it will float if too fast.

[One9iner]

Oh I'm sorry FlyKingfisher!! I was merely making a joke.Take it you're Sim time has never seen you further than the laptop??

[FlyKingfisher]

I had a go on MSFS a couple of weeks ago and the A320 did seem far trickier to land than the 737-800. It might be due to me having a better idea about the -400 but the control seemed vague at best.
Regarding speeds...slow down! by 25nm get 210 clean, 20nm get 190 flap 1, 15nm 170 flap5. It doesnt take long to travel...you are doing more than 3 miles a minute. Descend using PAPI or roughly 3 miles for every 1000agl.
Make sure speed is under control, it will float if too fast.

I feel the 737-800 is a lot more difficult to handle than the A320. Will keep your speeds in mind. Thanks.

Oh I'm sorry FlyKingfisher!! I was merely making a joke.Take it you're Sim time has never seen you further than the laptop??

Oh your sense of humour beat me completely. Perhaps my Sim time made me lose touch with the real world and my funny bone :hmm:

[Big_Mach]

As others have said 3x table is the key for a 3 degree glideslope (the usual descent angle even for visual approaches), so if you're straight and level at 2000ft above ground level you'll be wanting to go down at about 6DME (2000 x 3). In the real aircraft we start 0.3D before that because of inertia, so call it 6.3DME, and descend at about 700-800fpm, using the PAPIs to correct your trajectory.

That's assuming the DME is co-located with the ILS or is set for the threshold of the landing runway. Otherwise on the PROG page of the MCDU put "airport runway" in the distance box - eg EGGW26 would be distance to London Luton runway 26, LFPG09R distance to Paris de Gaulle 09R to give you a distance from the threshold.

Another trick is to use the Flight Path Vector (FPV) button on the MCP (just above the AP1/AP2 buttons). In fact that is the airbus recommended procedure for all visual flying.
That should put the "bird" up on your PFD so, once you've turned the flight directors off, have that sitting just below the 2.5 degree line and you should be going down at 3 degrees. Dial up the inbound course of the runway in the heading box of the MCP and once on the centreline, keep it lined up with the track line (little blue line on the horizon) and you shouldn't find yourself drifting because of the wind (sorry it's a bit hard to put it in writing but it should be quite straightforward).

As for speeds and config settings, obviously slow up early while you get used to the faster approach speeds, in fact I would initially suggest getting fully configured - i.e gear and flaps out before you start descending. When you're comfortable and happy with that, try 210/220 kts until the base turn or roughy 12-15DME if a straight in. Then Flap1 and let the speed bleed back to "S" Speed (approx 180kts) and Flap 2 just before you start to descend (obvioulsy this is dependent on tailwind, distance from threshold and ATC requirments). This is quite a good config because it stops the speed running away as you descend. If you have a tailwind or the thing isn't slowing up, drop the gear straight away, otherwise the usual procedure is to fly 160kts to 4DME or 170 to 5, then reduce the speed to Vapp, and as the speed is reducing take the gear, followed by flap 3 and Full to be in the landing configuration by 1000ft

You're aiming to fly Vapp all the way down to the threshold (we have a tolerance of +10/-5 kts otherwise we are unstable and have to go around). Depending on weight this will be in the region of 125-140kts. Too much over that and you have excess speed and hence excess lift in the flare so will float while the speed decays before smacking it down, too little and you run out of lift before you've landed and you smack it down!

I tend to cut the thrust between 20-30ft (generally closer to 20ft) and pull back slightly. You should be looking towards the end of the runway to get an appreciation of your closure rate with the ground, but simulators never land like the real thing (even full motion sims). If that's giving you a bit of difficulty, have a look at the instruments and at 20-30ft, slowly pitch up to about 6-7 degrees which should bring your rate of decent back to about 250fpm (I think!)

[FlyKingfisher]

@Big Mach: Thanks a million for your reply and the explanation. Will be of great help.

Another trick is to use the Flight Path Vector (FPV) button on the MCP (just above the AP1/AP2 buttons). In fact that is the airbus recommended procedure for all visual flying.
That should put the "bird" up on your PFD so, once you've turned the flight directors off, have that sitting just below the 2.5 degree line and you should be going down at 3 degrees. Dial up the inbound course of the runway in the heading box of the MCP and once on the centreline, keep it lined up with the track line (little blue line on the horizon) and you shouldn't find yourself drifting because of the wind (sorry it's a bit hard to put it in writing but it should be quite straightforward).

Yeah, I read this somewhere that during a visual approach, pilots change from HDG to TRK. That puts the "bird" up on the PFD. I've tried doing that, but since I'm not a qualified pilot and have no real flight training, I don't really know how to use it. But you've explained it well and I shall try to learn how to use this "bird". I fly visual approaches entirely on my own understanding of what needs to be done. The basics: first, slow down as much as possible; second, be fully configured to land before being cleared for the approach to avoid any last minute config changes which may destabilise the approach; third, initiate descent 6-7 miles from touchdown by keeping a rate of descent of about 600-700 fpm; keep the PAPI/VASI in sight to adjust trajectory and make adjustments to keep the aircraft aligned with the runway centreline. I just need to keep practicing. At least I'm not scared to carry out a visual anymore and I've stopped landing short/beyond the TDZ. The only thing I need to improve on, is the flare. I almost always end up smacking the aircraft down hard on the runway :ouch:

but simulators never land like the real thing
You are right. I guess we just have to make the best of what we have.