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

[safetypee]

The items in a stabilized approach ( FSF definition) 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_b...blizedappr.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...?

[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
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
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

[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

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?

[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

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.