Pitch-up Upsets due to ILS False Glide Slope
 

The Dutch Safety Board launched an investigation into an incident at Eindhoven Airport. During this incident, the flight crew of a Boeing 737 were confronted with a 'stick shaker' indicating an approach to stall condition. The flight crew made a successful go-around, after which the aircraft landed safely. The existence of false glide slope reversal emerged during this investigation, and was further analysed. Two reports have been published on the basis of the investigations: 'Stick Shaker Warning on ILS Final' and 'Pitch-Up Upsets due to ILS False Glide Slope'.


The report in English can be found here
Dutch Safety Board | Investigations & Publication | Pitch-up Upsets due to ILS False Glide Slope

An animation is here
https://www.youtube.com/watch?v=PxBoTMs_iEs

I cannot understand the comment that this 'phenomenon' was unknown to flight crew in 2013. There have been warnings about it for years and the advice has always been to capture from below if possible, and if not to monitor range and height to identify the false g/s. Also arming 'APProach' is NOT a good idea in this situation until on the correct slope.

It does appear to be a poor piece of controlling from Eindhoven ATC!

Edited for Speeling

Even the colonials are onto it! :D

http://www.airservicesaustralia.com/...up/a14-h14.pdf

BOAC,

I couldn't agree more. There's a pretty good reason to monitor height/distance!
I always hard tune a DME when I'm doing a GNSS/RNAV if at all possible.

A quick look at a European ATPL theoretical knowledge question bank (the stuff the teenagers learn) indicates that there is a possibility of false GPS lobes above the real GP.

Going back a few decades, a young CGB was told to beware capturing the GP from above.

I don't think it is about the the concept of a false glideslope itself but more the autopilot behavior that can result from it.
I guess everybody will be aware of false glideslopes but not the violent pitch up that is the reason of the investigation..…

Is new to me anyway. I would expect a pitch down or high rate of descent on a false glideslope, not a pitch up.

And sometimes you end up high and have to capture it from above. Just happens..

gys - in my 'time' we were warned that the land of reflected glideslopes was dragon infested, and it does not take much thinking to work out the effect of a reversed GS signal on an automatic system. Good that more now understand!

'Capturing from above' is part of the daily bread and butter for pilots - it just requires commonsense in use of the automatics - ah - if only....................:{

Going into Manila a long time ago and vectored high (4000 ft due noise abatement) to final ILS. Did the usual check of DME v height and it didn't tie in with the indicated glide slope. At 8 DME we should be close to 2500 ft if on slope. However, at that time we were above a low layer of stratus but at 3500ft due vectors. The ILS showed we were very slightly high on GS (quarter dot) when it should have shown full scale fly down.

We were Vref 40, no wind and on localiser with rate of descent well above normal for three degree slope. Became visual at 1500 ft with GS still showing slightly high but visual scene showed very high and obviously the glide slope we were on was around five degrees. All manual flying in the 737-200. As well, the T-VASIS was a dogs dinner all over the place. Landed and reported apparent false GS to ATC and crook T-VASIS indications as well. ATC advised they were aware of T-VASIS problem and that there had been recent earth tremors which had displaced the T-VASIS boxes. Hence incomprehensible light indications. However ATC SOP required the T-VASIS be switched on for all jet landings (regardless of serviceability!). No NOTAMs of course...

Some months earlier, an Air Manila (?) Boeing 707 had crashed short of the same runway with full flap, idle power and speed brakes extended. The 707 was a write off but minimal casualties I think. The captain swore he was on glide slope all the way from 15 miles out with no wind. Well he was but it was a false glide slope. But to maintain that glide slope he was forced into a high rate of descent about 1800 fpm hence full dirty up and idle thrust. They were fully visual too. Instead of going around, he pressed on regardless to see if he could make it OK. Asked later by investigators why he did not go around when well outside stable approach criteria, he said he thought the noise of the engines spooling up would scare the passengers :ugh:

Next day, after we reported our episode at Manila, a KingAir flight calibration aircraft tested the ILS and confirmed a flyable glide slope about 5.5 degrees (in other words a false glide slope). That is why the 707 pilot had to dive to fly the false glide slope and hard to believe the captain pressed on. In another life I flew DC3 radio navaid flight calibration aircraft in Australia. Part of the routine ILS test was to start at about 1500 feet on localiser at approx. 5 miles and maintain that height while observing glide slope indication. The test was to look for false glide slopes. It was common to see a false glide slope indication as we got closer to the threshold but these were at 50-70 degrees and of course quite unflyable. We did a similar test for false localiser indications by flying an arc across the localiser at 10 miles. False courses beyond 35 degrees from the localiser were normal and information published in the appropriate pilot documentation. There is no question in my mind that it is good airmanship to always be aware of DME v height cross check (where possible) during any instrument approach as well as a close eye on ground speed readings on short final.

The high angle false glide slopes were simply part of normal ILS glide slope characteristics and as you would need to be a Stuka dive-bomber to fly a 70 degree glide slope, they were of no flight safety concern. I was surprised to read on Pprune that the Eindhoven standard ILS calibration tests did not include a procedure for checking for false glide slopes as we did 50 years ago.

One cannot invent sufficient SOP's to bypass common sense.

Jeez - I'm not instrument rated - but that video is a scary watch...
Was completely unaware of this.

Many glide slopes need to be captured when using basic autopilots with care and airmanship. As soon as capture occurs from below the glideslope the autopilot will receive a pitch up command as you are still about a quarter dot below it. The 747 Classic was famous for it, at airports where the glideslope was captured beyond 9 miles.

Thought it was common knowledge.

It is important to make sure that the focus here is on the way the A/P responded (as designed!) to the reversed signals and not particularly on the rates of descent.

The other point is that there were a few clues missed by crew and ATC.

Afaik all 3 degree glideslope installations will produce a valid mirror slope at 9 degrees (6 degrees higher). I did fly one, in visual conditions, with a Dash 8. Worked...
Was a European airport with fairly modern equipment.

:confused::confused:
One of my first lessons on my UK IMC rating was to show a false G/P!! That's why most G/P's are only certified for 10nm and 3000ft!!

Safelife, the point that the DTSB is trying to make is that some installations may show a false glidespath at 6⁰. Most likely depending on wheather and other traffic in the neighborhood.

Also, very interesting to know how the AP reacts to not properly intercepting the glidescope from above... might not safe your underpants, but could safe the plane.

It is but a short step from a 'fly down' demand when 'below' the false GS (and going down) to the a/c trimming back to 'hold' the false G/S and then rapidly into a rapidly accelerating 'fly up' demand if at all 'above' the false GS. - I guess you would need to be 'there' to know. I suspect the rate of pitch was a touch high!

This has nothing to do with false glide slopes or whatever but all to to do with monitoring and being a pilot not someone carried around the skies with an autopilot.

If the aircraft is pitching up at slow speed to try and capture anything the pilot needs to notice that and correct the situation! its as simple as that

Again this is all to do with over reliance on systems WHICH ARE NOT 100% reliable and a move away from basic piloting skills which were more prevalent in the days where we were not lost in technological pilot aids

Agreed, but as per post#12 and it surely does no harm to 'refresh' those who have forgotten and educate those who apparently don't know? I do not see anyone excusing the crew or ATC.- this event would not have happened WITHOUT a false glideslope.

Not quite the same but do you remember the Air New Zealand 767 G/S incident in APIA?

Here is the link to YouTube

► 10:30► 10:30
Dec 22, 2006 - Uploaded by musicalaviator
An Air New Zealand 767 encounters a malfunctioning ILS Glideslope system which forces it ...

Excuse me, but what is a Final Approach Fix if it is not a confirmation of correct glide slope interception?

And another thing; how could one continue an approach below or beyond the FAF if never actually passing through it?