The Hedge

Hudson has raised this topic in a discussion re: the RFDS Mt. Gambier incident which is running on the GA forum.

I have rather scant knowledge of this phenomenen and was wondering if anyone has experienced faulty T-VASIS indications,where and the conditions in which it was encountered.

Cheers

Kaptin M

As posted on the same topic...high humidity/foggy conditions, can give full "fly UP/fly down" simultaneously.
Where?? Hobart in winter, on an otherwise crystal clear night, except for some shallow ground fog.
V V was perrrrfect - horizontal....deceptive.

hoss

Like Kaptin M, I have seen this in foggy conditions,though not as bad as he has.

Despite the drought there must be a fair bit of humidity at Canberra because I keep getting one dot high and one dot low at the same time on Rwy17 even in summer .

Safe flying, hoss

ps. The Hedge, if you use em, try jeppesen/air traffic control AU-320 note2 .

SmallGlassofPort

Adelaide Rwy 30 mid winter in mist/ground fog. Left Vasis showing 3 orange fly up, right 2 fly down.
Slightly offputting!!

Three Bars

Go to Jakarta (Soekarno-Hatta) and you'll get full fly-up/fly-down simualtaneously every day of the year - regardless of the weather.

Andu

I concur completely with the comment on the Jakarta 25R T-Vasis (or should that be the Jakarta “+” Vasis). I think we could get that fixed overnight if we pointed out to the Indons that they’re displaying a permanent, very large Christian symbol to every pilot who lands at Hatta.

OzExpat

hoss...

That's worth reporting to ATC, I reckon. There's a very fine difference between on-slope and 1-high, and also between on-slope and 1-low. However, it shouldn't normally be possible to see both 1-high and 1-low at the same time.

The techs should be able to fix the problem fairly readily.

hoss

Thanks OzExpat,I'll let them know next time .

Although,I'm not going to 'hold my breath'. It's hard enough to get them to change the ATIS let alone adjust a VASIS .

Safe flying, hoss

compressor stall

You might remember about a year ago I said the same thing about Cairns - one dot high and one dot low (and I am not talking about that Swedish bird from the Woolshed either ).

Well I did mention it to tower one day and Sure enough the next time I came in it was fixed.

Hugh Jarse

Hoss, I have to agree regarding CB 17. However, there was a paragraph in ERSA regarding erogenous indications on the T-Vasis RWY17. I don't subscribe to ERSA so dunno whether it's still noted.

I often see fly up/down on one side and the opposite on the other! And the VASIS goes dim at about 200'.

I thought I just needed glasses. Now I know you do, too!

Sperm Bank

Haven't been there for a while but Broome used to have bad indications at night with shallow fog present. 3 fly up, 3 fly down and on slope all at once. This is pretty much why other countries have given them away in preference to PAPI's.

PPRuNe Towers

Rob

The Hedge

Now that would be a distraction on final

olderairhead

This may surprise a lot of readers but the correct indication on slope is for boxes 3/4 and 9/10 (if dual) to be visible (but not full intensity).

This is due to the design of the boxes and the associated cutoff angles.

And also for information, it is the pilots responsibility to report any discrepancy on TVASIS and PAPI.

Both installations are only flight checked during commissioning. Ongoing maintenance is by ground crews and spirit levels.

As the subsoil movement can dramatically affect the site of the boxes, incorrect indications may result. If this occurs between ground checks then the techs rely on pilot reports.

OzExpat

HJ

I'd be reporting that - unless there's a note in ERSA about it.

oah

Well it sure surprises me! I've been doing 6-monthly flight checks on T-VASIS since 1986 and it has never been normal. I agree that the cut-off angles are very VERY close to the on-slope indication, but you should NOT see both lights 3 and 4 (and/or 9 and 10) at the same time unless, perhaps, the techs haven't levelled the boxes properly.

Hudson

Erroneous indications on all types of VASIS have been around for decades. When T-VASIS was first seen in Canada in 1973, this was via T-VASIS film. The Canadian Air Line Pilots Association were really keen on what they saw. In their letter to the Government of Australia Office in Montreal dated 12 October 1973, they said;

"A point of interest to all pilots and possibly DCA's Engineering staff has been raised by our members who are operating Lockheed L-1011's. They have noticed that the approach path on a VASIS (Standard) can be distorted -or refracted - when viewed through a layer of fog or low stratus cloud. This distortion or refraction is considered to be caused by the passage of the light beam through atmospheric layers having a heavy suspended moisture content. The distortion of the VASIS is below the flight path and could cause an aircraft to undershoot the required flight path".
............................................................ .......................................

Certainly during my own time at the DCA Flying Unit 30 years ago where I was involved in navaid and VASIS flight calibration, I saw this problem at first hand on the new T-VASIS installation for runway 20 at Townsville. The salt water spray particles from the nearby coast came to rest on the T-VASIS lights and caused remarkable errors as seen by the pilot.

While the Canadian ALPA referred to the early red-white system, I don't think it was realised at the time that under similar meteorological conditions the T-VASIS could also give dangerous information. Tragically, this may have happened at Mount Gambier.

The history of the introduction of PAPI into Australia is political. It was not introduced because it was thought superior in efficiency to T-VASIS. In fact there were a lot of DCA people against PAPI on the basis it was a colour discrimination based system and thus wide open to the problems described above. It certainly has very accurate cut-off angles but the T-VASIS advantage was that it afforded a better graduated rate of change and did not rely on colour changes.

But the T-VASIS needed more maintenance while PAPI was less expensive due less light boxes. That is the only reason why PAPI is here in Australia.

Now for an interesting piece of history. The designer of T-VASIS Mr Rob Cuming, arranged with the RAAF to help out with some flight testing of the first experimental T-VASIS which was set alongside Sydney runway 25. Cuming needed to get information on the flyability of the system at night over a wide range of speeds. The RAAF therefore provided a Sabre A95-358 flown by one of their Top Guns.

On 25 October 1961, the Sabre flew many approaches ranging from 120 knots to 300 knots. Due to traffic using runway 16, ATC asked the pilot to break early. At these speeds, it was difficult.

So the pilot said he could break UPWARDS. And so the Sabre was given the clearance to be ABOVE 4000 ft before crossing the intersection of 25 and 16. And spectators had the glorious sight of the Sabre pulling up vertically at night from short final on runway 25 and then half rolling back to another run in on the VASIS.

Now that's what I call flying!! That is a true story because the Sabre pilot is still around and read the sortie details to me from his log book today. Sortie time 55 minutes. The RAAF were thanked for their contribution to the T-VASIS experiments.

Good on yer HMJB AFC!!

olderairhead

OzExpat I also flight check T-VASIS, and my comment on it being normal to see the boxes mentioned is based on the mathematics of the angles. I too found this to be difficult to beleive until I saw the figures.

We had been reporting this event at the many of the installations around Oz and finally the issue was investigated. Unfortunately there are not that many people left in DCA/ASA etc who fully understand the true design characteristics of the system.

But find one we did. And the presentation we received forms the basis of my post.

Career Command

Humour: Ignoring humidity & atmospherics, perhaps the lawn maintenance people have bumped the boxes?

OzExpat

oah... the mathematics can cloud the issue a bit, especially if one looks at a Commissioning Flight Check report form in isolation. The acceptable range of angles, as shown in that form (and in the old Oz Flight Survey Manual) for light 3 (and 9) is 2.99 to 3.01 degees. Same for light 4 (and 10).

However, the way this angle is established is by flying the cross bar, one light low and then one light high. So the point I'm making is that it should be impossible to see both lights 3 and 4 at the same time. The occasional times when I've seen it, I've informed the techs, who made the necessary adjustments. A further run, tracked by the theodolite proved that the adjustment was correct.

As I understand it, this is the way that it was done in Oz many years ago. I'd be very disappointed if it's not being done that way these days.

CC...

Humour maybe but also, sadly, very accurate. Certainly in this dark corner of the world, anyway.

olderairhead

Oz we flight check with computer generated flight paths coupled to the EFIS, laser tracking, differential gps updating our position to within 2 cm both vertically and horizontally. Fairly accurate one might say.

We would be very disappointed if you don't do it this way these days.