Stabilzed Approach with white PAPI

[ranklein]

Hi,

Trying to find a law (FAA/ICAO), if exists, about taking into account the PAPI or VASI when determining whether an approach is stabilzed.Every place I find talks about other references (ROD, Speed, Configuration, Check List etc.).Nothing about PAPI/VASI.
Heard someone mentioning that one can descent at a 1000fpm max ,have an all white VASI or PAPI, but still be considered as stabilzed when crossing the 1000 (IMC) or the 500 (VMC) mark.

Any opinions..?
Regards!

[rudderrudderrat]

Hi ranklein,

If you do an ILS - then you should be in the middle of the VASI / PAPI.

If you do a NPA, then you'll sometimes find you're not in the middle, but well within the tolerance allowed. e.g. Check any LOC only (G/S us) MDA at the Missed Approach Point, then you'll definitely be in the all whites of the PAPI.

A landing from a NPA with the VASI / PAPI all white can be stable and safe - otherwise you'd have to be as accurate when doing a NPA as you are doing a full ILS Approach.

You won't be able to see the PAPI at 1,000 ft IMC.
Some NPAs have MDH below 500ft - so you may be in the whites when you become visual.

[Thunderbug]

I don't think stabilsed approach criteria comes from the law. For me it is laid down by company SOP. As part of that it states that stabilsed approach includes:

"On the correct vertical profile".

4 whites is not on the correct vertical profile - and with 4 whites you can't be totally sure as to how far off that profile you are.

1000fpm below 500' has to be called, unless it had been briefed for (i.e. a known steep approach)

T'Bug :ok:

[safetypee]

The items in a stabilized approach ( FSF definition (http://flightsafety.org/files/alar_bn7-1stablizedappr.pdf)) provide guidance for operators and can be to adapted for specific operations. Thus, unless regulators require a stabilized approach to be flown within specific constraints, there is no ‘law’ specifying the details.

The principles of a stabilized approach require that a safe flight path be defined and that the defined path be established before some minimum altitude.
For a precision approach (ILS) there are existing conventions which define safe boundaries for the flight path, e.g. 1 dot deviation. PAPI/VASI deviations would correspond with these.
As above, 4 whites on the PAPI would not be within the boundary of the required flight path.

For a non-precision approach (those having higher risk) the flight path should ideally be a continuous descent based on prevailing conditions. The flight path can be defined with airspeed and the vertical rate. Safety boundaries should be specified for each of these, e.g. +/- 5 kts, +/- 200 ft/min.
In some tailwind conditions at high approach speeds, it might be possible to expect a VS of 800 ft/min, thus a limit at 1000 ft/min would just satisfy the stabilized approach criteria; but I would be very cautious of operating in such situations.

[BOAC]

ranklein - most definitions of 'stable' include reference to some sort of (undefined) power setting which can be considered 'normal' for approach. All a bit vague - like so much - but remember that a very steep approach might be considered 'unstable' if, for example, the levers (engines for AB folk:)) are on the idle stop (near flight idle for AB folk:)) at the gate.

[Intruder]

Trying to find a law (FAA/ICAO), if exists, about taking into account the PAPI or VASI when determining whether an approach is stabilzed.Every place I find talks about other references (ROD, Speed, Configuration, Check List etc.).Nothing about PAPI/VASI.
Heard someone mentioning that one can descent at a 1000fpm max ,have an all white VASI or PAPI, but still be considered as stabilzed when crossing the 1000 (IMC) or the 500 (VMC) mark.

Any opinions..?

In IMC, the PAPI and VASI aren't a factor, because they won't be seen until significantly after the point where a stabilized approach is required (generally 1000' AGL).

In VMC the PAPI or VASI may be used for further guidance, but the vertical speed allowed in a typical stabilized approach (2000 FPM from 2000-1000' AGL; 1000 FPM below 1000' AGL) will normally be more than that required for a 3 deg glide slope. Therefore, a "white PAPI" is acceptable if corrections are being made and/or a normal landing can be made from the approach. Otherwise, any pilot would have to go around any time he deviated above the glide slope (for the PAPI) or below the glide slope (for the regulations).

FWIW, I consider 40% N1 as the minimum acceptable for a "stabilized approach" in the 747 (GE CF6 engines).

[Centaurus]

If you do an ILS - then you should be in the middle of the VASI / PAPI.

Not necessarily so. The siting of the ILS glide path transmitter may not coincide with that of the VASIS/PAPI installation. In addition, some PAPI/VASIS light signals are set for long body types with typically a 71 ft TCH, whereas normal ILS TCH is 51 feet.

[rudderrudderrat]

Hi Centaurus,

I agree and the difference will become apparent when very close to the runway. I don't think 20 feet difference at the 500 ft gate will be significant though.

[PappyJ]

...Nothing about PAPI/VASI...

I quite strongly disagree. The various references to "stabilized approaches" including the link posted earlier http://flightsafety.org/files/alar_bn7-1stablizedappr.pdf all list the number 1 criteria as "The aircraft is on the correct flight path"

Flight path is always defined as both Horizontal and Vertical. Maintaining a VASi, in the absence of an accurate ILS system, would certainly fit the requirements of "...correct flight path..."

[billteasdale]

One thing I don't see discussed is the relativity of what constitutes a stabilized approach. Within SOP is a given... but a low time in type pilot needs to be on a much more accurate profile (i.e. centered on the PAPI/VASI) and completely set up in landing configuration, while a more experienced in type pilot can accept a bit more, for lack of a better word, slack, in the parameters (e.g. all whites, thus high on approach and possible long touchdown on a suitable runway/airstrip) Of course, SOP must be the governing principle, as well as operating regs (135 or 121) in a given country as well as the registered country of the aircraft.

I think that, at least in the FAA, the "rules" are intentionally centered around an operators approved SOP's, to allow for this sense of relativity.

But, as always, "Aviate, Navigate, Communicate", and when in doubt, go around and reset.

[Jim Croche]

Re "Stabilised" don't forget that with the Airbus thrust system, thrust at IDLE (using Managed speed) may well be an appropriate thrust condition that complies with the Stabilised requirements at 1000ft if Ground Speed Mini is active. For non-Airbus drivers, Ground Speed Mini is s system that attempts to control the energy on the approach by ensuring a minimum ground speed at all times depending on the wind being experienced at any given time.

[Green Cactus]

To get back to the initial question (as I understand it..), can you be stable while above the vasi/papi.

I see no reason why not, as long as you determine that you will not have to make power/pitch/configuration changes to maintain the desired vertical path, and are able to maintain an appropriate minimum power setting.

It is the same situation as not having a visual vertical guidance, only steeper.

It is nowhere published that 3 degrees is the holy grail, It might be smart to use as you are familiar with the "picture".

As one of the earlier contributors mentions, when new on an airplane stick to basic/known situations, once you become familiar with an airplane you can give yourselves some more "slack".

GC

[capt. solipsist]

err.., guys, why hasn't anybody raised the issue of AIMING POINT (retention) here...? :ugh:

[plain-plane]

You are flying a tail wind approach at i.e. on a 3,5 deg ILS…. That will give you close to 1000fpm, and there are also 4,0 deg glide slopes out there…
(And no, you are not doing at tailwind app to a higher deg. glideslope than normal because it is your first choice)

And also check that glide slopes coincides with the ILS… some military airports have all kind of funny papi installed, 2,25 deg , 2,5deg and so on. Some places even have two different papi set up, one left, one right of the RWY.

Popping out at minimum at night and seeing all those white papi at night does tend to make you focus at bit, even when fully briefed…

[de facto]

Capt Solitist,

Thanks for the info on the bleeds solenoid:E
Regarding the 'definition' of a stabilized approach I believe all was mentioned above.
I remember being taught, Red over White: You are allright
White over white: Wake up!
Red over Red: You are DEAD:eek:
Airports like NICE, do have their papis set for the big Boys/girls(B747), so on the glide you will see 3 reds and one white.(in your 737).
Once you transition off the papis, yes yes go for the AIMING markings on the tarmac...

Being stabilized VFR with thrust in ,configured,correct ROD,,,but overhead the threshold at 500 feet is not stabilized:8

[Denti]

Actually, flying 3 red one white simply means you approach at a shallow angle to the same aiming point. It does not mean you will touch earlier and actually tends to increase the landing distance according to our QAR program.

[de facto]

Denti,

I wrote if you follow the glide path (Ils), at a preset path angle, in a B737 you will see 3 reds and one white as the papis angle is set for larger aircrafts.
If you decide to follow the papis when visual (lets say from 500 feet to threshold) and go for 2 white/2 red your aircraft will be maybe about 80 feet above threshold rather than the usual 50 ft.

Ducking below the glide in the last hundred feet (ie trying to make a short landing),you will as you said make a longer landing as the flare will be increased...hence your QAR readings.

[aterpster]

billteasdale:
One thing I don't see discussed is the relativity of what constitutes a stabilized approach. Within SOP is a given... but a low time in type pilot needs to be on a much more accurate profile (i.e. centered on the PAPI/VASI) and completely set up in landing configuration, while a more experienced in type pilot can accept a bit more, for lack of a better word, slack, in the parameters (e.g. all whites, thus high on approach and possible long touchdown on a suitable runway/airstrip) Of course, SOP must be the governing principle, as well as operating regs (135 or 121) in a given country as well as the registered country of the aircraft.

In the U.S. we have a regulation that requires a commercial operator to touchdown within the touchdown zone.

We also have more and more instrument approach procedures with vertical guidance (especially LNAV/VNAV, LPV, and RNP AR) where the chart is noted: "VGSI and RNAV glidepath not coincident."

The pilot, regardless of experience level, is well-advised to follow the glidepath rather than the VGSI in such cases, for any number of reasons.

[de facto]

Aterpster,

Last time I asked the boeing guys why they dont call for a Go around maneuver(ie unstabilized approach) when pilots touch down passed the touchdown zone,I was told it is captain decision:rolleyes:

Quote:"VGSI and RNAV glidepath not coincident."

The pilot, regardless of experience level, is well-advised to follow the glidepath rather than the VGSI in such cases, for any number of reasons.Unquote.

Could you please elaborate?:8

[aterpster]

de facto:

Last time I asked the boeing guys why they dont call for a Go around maneuver(ie unstabilized approach) when pilots touch down passed the touchdown zone,I was told it is captain decision:rolleyes:

Quote:"VGSI and RNAV glidepath not coincident."

The pilot, regardless of experience level, is well-advised to follow the glidepath rather than the VGSI in such cases, for any number of reasons.Unquote.

Could you please elaborate?

Those Boeing guys need to read FAR 91.175 (c)(1). Further, most U.S. carriers further define a more restrictive permissible TDZ; one for narrow bodies, another for wide bodies.

As to the RNAV glideslope that leads to a decision altitude that path often provides a more optimum TCH than does a VGSI. Also, in many aircraft the VNAV glideslope can be coupled, thus assuring a stablized descent path to DA if not the threshold. And, in marginal visibility conditions the VGSI can be indistinct in the visual segment, especially in the daytime.

Further, if the RNAV glidepath differs from the VGSI path, transitioning from the RNAV glidepath to the VGSI path at low altitude can tend to destablize the aircraft's vertical path at a critically low height.

[de facto]

Aterpester,

I understand and agree that Precision approach aids are more precise than visual aids such as papis:8
If one flies an ILS,the glide slope is the most accurate but Papis should be monitored as well,as they give an easier,less precise guidance than the glide slope at low altitudes.(it was mentioned earlier,that new pilots may find easier to follow the papis in the last 500 feet than the glide)..

If one flies a VNAV app,the papis should also be included in the scan for cross checking(distance versus altitude).

If one flies a Visual, the Papis provide the best guidance when turning final.

If one flies a non precision app (Vor,Ndb),the papis provide the best guidance until distance to threshold is such that the aiming point is clearly identified and followed.

Also, the Papis position (left or right or runway) should always be briefed(especially during non prec.app)as they will give an additional clue that you are aligned with the correct runway.

Knowing if the papis for the runway you will use are calibrated for 747 will give you an extra clue as whether to follow them precisely until approaching the threshold or if an earlier transition to the aiming point is more adequate.

I hope that clarifies my previous posts and general idea on the subject:)

[aterpster]

VGSIs are invaluable when the approach does not have a DA for the landing runway.

Since you bring up the finer points about VGSIs, it is also important to determine whether there is any restriction to its customary maximum useable distance and angle of coverage especially at night and/or in restricted visibility conditions.

[Checkboard]

The stabilised approach criteria in my current airline specifically excludes PAPI from the definition in order to allow for approaches not coincident with the PAPI slope.

A case in point is the RWY05 VOR/DME approach at Geneva, which due to terrain is quite a bit higher than the ILS & PAPI. On the VOR/DME correct profile, at the minima, you will have 4 whites on the PAPI - but under our definition this is "stable" and you may continue to a landing.

Interesting about the USA FAA rule regarding touch-down zone. In Australia the company had an SOP about the touch-down zone, but my UK airline seems to ignore it completely in their manuals and operation. A mistake IMHO.

[aterpster]

Checkboard:
A case in point is the RWY05 VOR/DME approach at Geneva, which due to terrain is quite a bit higher than the ILS & PAPI. On the VOR/DME correct profile, at the minima, you will have 4 whites on the PAPI - but under our definition this is "stable" and you may continue to a landing.

I can't speak to PANS-OPS in this case (which is generally more conservative than TERPs) but such approaches that have straight-in minimums under TERPs cannot exceed a final segment descent gradient of 400 feet per mile (3.77 degrees) to the runway. Once within the distance of VGSI coverage, and visual, an adjustment to capture the VGSI generally won't de-stabilize the approach and has the added benefit of not crossing the threshold excessively high.

Often those types of VOR approaches are offset from the runway so there has to be a lateral maneuver once visual.

[de facto]

Quote:'Once within the distance of VGSI coverage, and visual, an adjustment to capture the VGSI generally won't de-stabilize the approach and has the added benefit of not crossing the threshold excessively high.

Often those types of VOR approaches are offset from the runway so there has to be a lateral maneuver once visual.'unquote.

I agree.
Having flown to Innsbruck in Austria on B737s,the Loc approach on Rwy 26 would lead you to an MDA,but then a visual segment was required(slight left turn)to intercept the runway centerline.Therefore allowing extra room to lose some altitude and follow the papis once established on final.
Using a VDP would allow a more standard rate of descent at low altitude.

I have never flown to Geneva but I am sure if you do a non precision approach there and continue to the published MAP,you will be high on final,therefore the importance of defining your VDP before the approach and then be able to continue with the same rate to establish on the papis.

[Denti]

As to the RNAV glideslope that leads to a decision altitude that path often provides a more optimum TCH than does a VGSI. Also, in many aircraft the VNAV glideslope can be coupled, thus assuring a stablized descent path to DA if not the threshold. And, in marginal visibility conditions the VGSI can be indistinct in the visual segment, especially in the daytime.


Do you talk about baro VNAV here? Or similar concepts as Boeings IAN? If so, you need to be extremely cautious as baro-VNAV is not known for its precision, even half a hP is around 15 ft different TCH at sea level, more at higher airports. Since the reported QNH is only in full hPs and only every half an hour you can have quite a few feet of difference between the correct glidepath and the displayed one.

Granted, it looks very precise, especially if you have the same indication as on any precision approach (ILS/GLS), which is the standard on 737s now. However you have to be aware about the pressure and temperature effects on FMC derived glidepath indication. Something that PAPIs do not suffer from.

[aterpster]

Denti:
Granted, it looks very precise, especially if you have the same indication as on any precision approach (ILS/GLS), which is the standard on 737s now. However you have to be aware about the pressure and temperature effects on FMC derived glidepath indication. Something that PAPIs do not suffer from.

No doubt that temperature affects Baro VNAV (except for the compensated systems). But, if Baro VNAV is the only IAP certified glidepath option, it is a whole lot better than no vertical path. And, becoming visual at typical minimums its errors are minimal and its better to stay with its stable path than attempting to transition to a VGSI.

Finally, Baro VNAV systems in RNP AR qualified aircraft have to perform to some very tight requirements.

[Denti]

They are very precise as long as the input is correct. However they do suffer a lot from input derived errors. If you have due to pressure change within the time between ATIS-cycles an input error of just one hPa it might make landing on a marginal runway impossible if you follow the GP for too long. Which is the reason why Boeing changed our SOP to only continue visually below any MDA/DA on IAN approaches, the GP is not longer deemed safe below that.

Of course any GP is better than no GP, which is exactly why IAN is such a great tool since it offers a GP for every kind of NP approach, but it remains still a non precision tool with all its limitations. Non-Baro non-ILS precision approaches are something completely different and of course something we hope to see a lot more in the years coming. GLS to CAT I limits is allready operational and we are currently in the certification process to CAT IIIa limits, which makes sense since boeing offers GLS as standard equipment on current aircraft.

[aterpster]

Denti:
They are very precise as long as the input is correct. However they do suffer a lot from input derived errors. If you have due to pressure change within the time between ATIS-cycles an input error of just one hPa it might make landing on a marginal runway impossible if you follow the GP for too long. Which is the reason why Boeing changed our SOP to only continue visually below any MDA/DA on IAN approaches, the GP is not longer deemed safe below that.

I don't believe we are speaking of quite the same thing. I am making reference to a Baro VNAV path that is locked in the nav database as part of the instrument approach procedure, not a path constructed by the flight crew.

[RAT 5]

I accept that this might be deamed a slight digretion, but I do so anyway. Firstly I have to assume that 3 reds or 3 whites = .25 degree deviation from 3. Thus if you are JUST on 4 whites you are 0.5 degrees from 3 = 3.5 and JUST on 4 reds = 2.5 degress. There is an airfield I frequent where the PAPI's for the circling rwy are set at 2.5 degrees. Our circling procedure is designed to roll you out on finals at 3 degrees. The circling MDA could be as low as 400' agl. & the vis 2400m. The landing gate is 300' and for SOP's you have to be 3 reds or 3 whites at worst. You roll round on finals at MDA and min vis. You see 4 whites. You've got 100' to make the correction, but not at >1000fpm. It's all workable, but it gives the F/O as PM a fright unless you brief it. One solution is to extend the downwind by 5secs to create 3 whites at worst.
However, back to points raised above; you roll out stable on 3 degress, constant aiming point, constant speed, constant power all correct for 3 degrees, but 4 whites. At first it is confusing. Should PM call a G/A? That's their dillema.
Equally, 4 reds becomes a G/A which at some point must transit through 2 whites 2 reds i.e. correct Glide path; so why not make a sensible adjustment rather than a mandatory G/A. Surely Mk.1 eyeball can tell how low you really are, unless of course there is hight ground descending in the undershoot. The same true for 4 whites, Mk.1 eyeball. Could it be that most C.P's don't trust visual judgements anymore? And what would you do on minimum fuel at MDA at a non-radar airfield?
All I'm trying to say is perhaps the answer to the original question is not so red & white. As is much of aviation. We've just been brainwashed into thinking so.

[Denti]

I don't believe we are speaking of quite the same thing. I am making reference to a Baro VNAV path that is locked in the nav database as part of the instrument approach procedure, not a path constructed by the flight crew.

Actually, that was what i was talking about. Purely database derived approaches, it is not VNAV anymore with boeing as that is old fashioned and put to rest in favor of IAN which behind the scenes is the same thing.

Baro VNAV still relies on baro settings and only can be as precise as those. And baro settings are inherently inprecise, unlike purely geometrical approaches like GLS, MLS or ILS. One hPa equals roughly 30ft in height difference at sea level and that is something you will have quite often during rapidly changing conditions. Crossing the threshold at 80 ft (50 plus 30 for one hPa) will increase your landing distance with picture perfect flying by around 200m in a 737, which on a marginal runway could be outside limits (mandatory GA). That is why boeing advised us that the database derived glidepath might not be a good idea to follow below MDA/DA and that segment should be flown visually only, GPWS "glideslope" alerts can then be ignored as they are very common.

Don't get me wrong. Baro VNAV is a nice tool, but one has to be aware of its limits.

[aterpster]

Denti:

The chairman of the FAA/Industry performance based navigation committee (the PARC) is a Boeing engineer. Also, there is another Boeing engineer who represents Boeing on the PARC. It they have discussed this recommendation to not use the database BARO VNAV glidepath below DA, I must have slept through it.

It's now on my question list. :)

[Denti]

Yup, should be interesting. As i said, boeing required a training change to only fly visually below MDA/DA if using Baro VNAV from my company. By the way, it is also very interesting to see the vertical ANP which is constantly displayed on a 737. Haven't seen any value smaller than 40 feet yet which seems to say the same thing as the boeing requirement.

By the way, you might ask them why they are not going for GBAS instead? Covers 50 precision approaches up to CAT IIIb capability within 25 NM around the station, one station costs less than a single VOR.

[aterpster]

Denti:
By the way, you might ask them why they are not going for GBAS instead? Covers 50 precision approaches up to CAT IIIb capability within 25 NM around the station, one station costs less than a single VOR.

I know the answers to that one, at least for the FAA jurisdictions and the U.S. carriers.

1. The FAA is overwhelmed trying to get WAAS become an effective program for other than week-end light tin. Also, their rudder is broken on their NextGen "ship."

2. The airlines can't afford Boeing's or Airbus high, high prices for any avionics retrofits.

[Denti]

Hmm, doesn't sound good then. However, at least on 737s GLS is standard equipment if you get new ones which i think quite a few US airlines do. Shame to let it go to waste except for that one test installation in Memphis. Well, over here in the old world WAAS won't be approved for precision approaches soon, and certainly not for CAT II or higher.

[Jax0510]

What does this mean, I was told that if you are fully coupled to an ILS this approach would take you just short of the runway threshold, I need a reference where I can look this up. Thanks

[galaxy flyer]

Jax

Look at the back side of the Jepp Airport Chart (10-9), there is a listing of all the distances--Glide Slope touchdown point is about 1300'-1500' feet from the threshold, TCH on the GP is around 45'-55', so where did you learn that a coupled ILS touches short of the pavement?

The electronic and visual paths may not coincide because that are not collocated on the runway side.

GF

[Crossunder]

There are really only two things that matter when it comes to the final apch and landing: Where do you want your wheels to touch the ground, and at what speed? Boeing says 1.000ft from threshold, at Vref. That is all you need to know. As long as your ROD does not trigger the EGPWS and your colleague's gluteux maximus are not excessively flexed and still in contact with the seat, you should not worry much about the PAPI, as it usually intersects the rwy 1.000-1500ft down the rwy (and then you must flare).

B737 FCTM p.6.6 v.June2010: "The PAPI may safely be used with respect to threshold height, but may result in landing further down the runway."

Find your aimpoint and make the aircraft fly towards it at the correct speed. Basic piloting skills.
My point? If the chief pilot says you MUST fly PAPI down to 50ft in order to be stabilised - show him the OM page where it says that safety is always priority #1. I have seen sooo many pilots struggle to fly that damn PAPI all the way down, working the controls like a damn foosball game and completely forgetting all their basic PPL skills of pitch, power and aimpoint. The flight path usually ends up resembling the path of a sewing machine pin, ending in a grand last-second panic "adjustment" to get back up on the PAPI. This adjustment is usually too aggressive, and we end up whizzing past the PAPI with excess speed and lots of runway behind us. Then you add a limited, slippery runway to that. Aimpoint aimpoint aimpoint and then slam that sucker down before you set a new world record in floating.