Incidents of Erroneous Glidepath

[OzExpat]

Back in 2000, Air New Zealand flight 60 encountered an erroneous glidepath on RWY 08 ILS at Apia, Samoa. I've studied the 203 page report of this incident and found a reference to a similar incident at Rio De Janeiro, in 1999. I've searched high and low throughout the world wide web and can find no reference to it.

This seems strange because, the abovementioned NZ 60 report shows that both Boeing and the FAA were aware of it. Can anyone point me in the direction of the report on the Rio incident please? A URL would be great, but I'd settle for a knowledgeable independent account of it.

My web search brought up something that appears to be a similar incident in Italy, involving an Alitalia flight. The problem is that the report sems to have been written in Italian, which is not a language that I know anything about. Has anyone heard of an incident like this in Italy?

Is anyone aware of any other incidents of erroneous glidepath? I've found an ALPA comment about an erroneous Localiser, in Africa, and it would seem that such incidents aren't as uncommon as they should be. But I'm more interested in the glidepath, as I'm trying to do a report for my own masters (PNG CAA) on the frequency with which erroneous glidepath incidents have occurred.

Any help at all will be greatly appreciated.

[Captain Stable]

What's the URL of the Italian report, OzEx? Have you tried feeding it thru a translator?

[OzExpat]

I ddin't keep a record of the URL CS because there's nobody I know around here who speaks Italian. I've just tried a few different searches but can't find the reference so don't even know how I phrased the search query that turned it up.

However, on the off-chance that someone reading this forum speaks Italian, I'll keep looking for that report.

[Groundbased]

Oz,

The Rio incident involved an Air France 777 in feb 1999.

There is a description of the incident at www.flightsafety.org in the flight safety digests for July 2002. You have to register to get the stuff but its free. They also mention the air NZ incident and a couple of others. I have never seen a full report on this AF event and would be interested if you find one.

Also think the Boeing aeromagazine had an article about erroneous glideslope indications recently.

Cheers,
GB

[OzExpat]

Thanks for that Groundbased. I found the FSF website but didn't register as I thought it would either cost money or require me to demonstrate my qualifications, or both. I didn't particularly want to have to give out any personal type info on a website, so I shyed away from registering.

I've taken your advice and registered and also found and downloaded the article on Erroneous ILS. Thanks very much for that.

My previous search found a reference to Erroneous GP on the Boeing site, but it was impossible to identify which specific article it was from the ones they listed. I couldn't afford to stay online long enough to check thru them all.

But, thanks to you, it looks like I've got the information I was primarily looking for. I'll keep an eye out for the official report, though I don't know which mob would've handled the investigation... maybe that'll be made clear when I get to read the FSF material a bit later today.

[PaperTiger]

If you can read Portuguese, the AF GIG incident is also discussed here (http://www.geocities.com/aviatorebr/Article_ILS_BCA.htm) .

[flapsforty]

EggSplat, my mate Flyblue is Italian and I speak the language.
Between the 2 of us we could probably come up with a credible translation if you really want to read that report.

It'll cost ya though... ;)
xxx

[flyblue]

It should be the AZ Zurich accident you are talking about. As Flaps says, I'll be glad to help if you need it.

We take credit cards ;)

[OzExpat]

First up, my sincere and grateful thanks to forget who contacted me by PM and e-mail with a great amount of very useful information. Also, again, to Groundbased, as I've now read thru the FSF article that he told me about. Lots of very good, if somewhat alarming and even frightening, information.

PaperTiger... thanks very much for that. I received the English version of that from forget, but I'm grateful to you for helping me to cover all the bases.

Flappy... I can never resist you and I won't deny you anying! http://www.pprune.org/forums/images/icons/46.gif

flyblue

We take credit cards ;)
Do you return them too? :D

The good news is that I found the site that I was looking for. Right now, I'm just hoping that I correctly identified the language as Italian... :O Anyway, the URL is at the Airmanship Online (http://www.airmanshiponline.com/fall2000/10-MXP%20luglio92.htm) web site.

Now then, Flappy and Flyblue... please be gentle with me... my boss's budget isn't very big... :D

[flyblue]

have a look (http://www.airmanshiponline.com/fall2000/11-MXP%20July92%20english.htm) ;)

[OzExpat]

flyblue... thanks for the very rapid translation! How on earth did you manage to get it up on the same website so fast! ;) Thanks for finding the English version of the page for me, I don't know how I missed that salient point.

It is precisely the sort of report that I'm looking for too, so thank you very much.

[flyblue]

Welcome! :)
Regarding Rio, I think it is the, er :( , Air France B777 incident in 1999 in Rio de Janeiro. Try and post in the French Forum.
I will try to get info too.

[OzExpat]

Thanks flyblue, I have a report on the AF incident at Rio, from the FSF website and now have an enquiry in with AF about the official report. I'm also chasing leads on incidents in other parts of the world but, in my haste in reading this thread, I'd overlooked your comment relative to "the AZ Zurich accident".

The only prang that I'm aware of there was in 2001. It involved Crossair Flight LX3597 from Berlin/Tegel to Zurich - RJ100 rego HB-IXM. Are you thinking of that one, or another?

[flyblue]

should be this one (http://aviation-safety.net/database/1990/901114-0.htm)

[PaperTiger]

You have of course read Band of Brothers by Ernest Gann, haven't you ? ;)

[OzExpat]

Oooooh, ouch! That's a very different one to the the one I was thinking about blue. Sadly, not enough info to suggest the involvement of an invalid GP, so can't use it in me report. Thanks anyway.

PaperTiger... "Ernest Gann"? Hehehe. No, I don't like to be made completely miserable. I know there's lots of good info in "Fate is the Hunter" tho!

[CI300]

The KAL loss at Guam might be worth a look too. btw i have a small role in the nz60 video.

[OzExpat]

Yes thanks CI300, the Guam prang is among those that I'll be reviewing. The really sad aspect of this whole problem is that there may be many more accidents and incidents, stretching back over the last 50 years or so, where invalid ILS signals, of one sort or another could've been an unrecognised causal factor. We may never know of all the occurrences.

Unfortunately, I'm not in a position to acquire a copy of the NZ60 video.

[OzExpat]

In addition to the Apia incident, I now have information on events that involved invalid LLZ and/or GP signals at :

Rio;
Madrid;
Rabat;
La Reunion; and
Cranbrook.

I also have information on the Guam CFIT. I can't yet conclusively link the Guam prang with invalid GP data because of the action of the aircrew, as evidenced from the CVR but, if I add this to the list, it makes a total of SEVEN events since 1997. This is disturbing, most especially because I feel that insufficient action has been taken to prevent the problem, or even to minimise the residual risk.

However, does anyone have information about similar events at other places around the world. I have an oblique reference to an incident at San Francisco, date unknown, that may have occurred while ILS flight calibration was in progress.

[Centaurus]

Manila runway 24 ILS was a place where the glide path was dodgy on occasions. One day we were radar vectored high on 7 mile final and expected to see full scale fly down on ILS. Instead the needle showed just a fraction of a needle width high with rate of descent and DME versus height indicating a false glide slope indication in the region of five degrees.

A few months earlier a B707 had crashed just short of the same runway due to a high rate of descent all the way from 20 miles out. The pilot swore that he was on glide slope. He probably was - but on a false glide slope which was later confirmed by a calibration aircraft to be five degrees.

[Tinstaafl]

Oz, by 'false glideslope' are you referring to one of the side lobes that are often present, or to the primary lobe being misaligned?

I'd always understood the spurious side lobe issue is countered by an 'on G/Slope' + height/distance check at the both the FAF & markers.

[BOAC]

I'm fairly well convinced that a lateral ridge under the slope can 'deflect' the glide upwards, giving higher than normal descent rates until crossed - eg ?GVA R05 and AGP R14? - but as Tinstaafl says, check range v height.........

[OzExpat]

Centaurus... Do you have any idea how I might find out more about that B707 prang at Manila?

Tinny... No mate, I've been deliberately using the terms "invalid" and "erroneous" to differentiate between this problem and the more widely known "false" indication. A "false GP" is one caused, as you quite correctly state, by side lobe signals. Theoretically if you intercept it and could follow it, it would still produce the normal GP angle of descent.

An "invalid" or "erroneous" GP, OTOH, is quite different in that it is only present during maintenance work, or during certain calibration activities. The radiated signal is deliberately skewed, to test various signal parameters and this is done by navaid technicians. They are supposed to reset the equipment after those activities.

Sometimes they forget to do so. Even then, it only becomes a significant problem if the relevant monitors in the ATC facility are U/S, because then ATC depends on the techs to tell them when they're mucking around with the signal. Sometimes, this communication doesn't occur.

The event at Apia had all these things conspiring at the time and, worse still, the navaid tech's own monitor had been left in "bypass" mode so that it couldn't automatically shut down the defective GP Tx and transfer control to the standby Tx.

You don't counter a spurious side lobe by means of altitude and distance checks, because (all things being equal) it will still produce a 3-degree (or so) descent path. You counter it by ensuring that you're inside the capture zone of the true GP signal. Instrument approach procedures generally account for this n one way or another and ATC radar vectors are another line of viable defence.

BOAC... I would hope that things like that are detected during the ILS commissioning, or periodic inspection, flight checks. Procedures can then be developed to get around the problem, one way or another, and ensure that pilots are aware of it.