US Navy 7th fleet at the time of LHR disaster.

[Sarcs]

The approach was kept in service for another 4 years after the accident because there was nothing wrong with it.

If 'there was nothing wrong with it' how come TAWS units (compliant with ICAO approach designs) in various aircraft were pinging South Pap? See here:
http://www.atsb.gov.au/media/1358144/ai2007010.pdf

[compressor stall]

Because the PANSOPS design requirements for instrument approaches and the various triggers for GPWS rely on different information.

An instrument approach design gives you a distance from a point (e.g. the paps) and wouldn't care if it was a 1 inch knoll on a plateau or the point of a matterhorn.

The GPWS looks at (amongst other things) closure rates on terrain, and would be looking at the rate of closure of the side of the steep mountain towards the aircraft but does not have the brains to know that the mountain will actually stop some hundreds of feet below the aircraft.

[Sarcs]

Stallie I basically understand the principles of a GPWS/EGPWS that you are saying, although I think the 'nuisance warnings' in the ATSB report were deriving their information from the RADALT. However does that excuse leaving the approach in service for 4 more years? Maybe they were just waiting for the PAN-OPs instrument design requirements to change so they no longer had to consider the Mount Tozer spot height, who knows?

You would also think that the aircraft flown to certify the approach would be equipped with the latest and greatest for the time (1999), so at least a GPWS, they then would have had experienced the nuisance warnings themselves and adjusted the approach accordingly!

[alphacentauri]

Sarcs, Not all GPWS systems are created equal. Each manufacturer can use slightly different algorithms to interpret terrain differently. It even comes down to what terrain database they are using and and how the algorithm interprets rate of closure.

I believe at LHR quite a few GPWS were used to test the approach and only some of them sounded a warning. I am pretty sure the CASA test aircraft GPWS didn't sound a warning, but I do know that the RAAF one did.

This scenario has also causing some issues at Gladstone. This was solved with the GPWS system in question needing a terrain database update.

In short, a precedure is not pulled if it satisifies the criteria of the day and is test flown as suitable. Just because some systems sound a warning doesn't mean the procedure needs to be withdrawn/redesigned. It more than likely means the system is too outdated or not refined enough to deal with these types of terrain issues. The problem is at the system end, not the procedure end.

[Sarcs]

So alphacentauri, since you seem to know so much about this, do you know what aircraft and equipment was originally used to certify the original LHR RW12 GNSS RNAV approach?

[advo-cate]

GPSS-NPA Design

So Alpha, what you are saying is:

There has never been an error in a plate??

Some other questions:

General Plate Design:

1. What is the procedure for example where there are other approaches for the missed approach
2. If there is a NDB and a GNSS-NPA, are the missed approach paths designed for no confliction?

[alphacentauri]

The aircraft used to validate the original procedure was a Navajo, to the best of my knowledge it was not equipped with GPWS. There was and is still no requirement in the certification process to assess GPWS warnings, although it is brought to CASA's attention if one is found to alarm during a flight test. Further investigation usually results until the regulator is satisfied for publication.

The GPWS tests I alluded to in the above post were after the incident.

There has never been an error in a plate??

Advo-cate...did I say that? Has there ever been a procedural error? I would nearly say 100% no. Has anyone ever hit something whilst flying the published IFR procedure? There are quite alot of checks and test flying of procedures before they are let loose and the current rounds of checking are flown by pilots who actively fly in GA and they have to sign the certification.

In answer to your questions, consideration is given to surrounding procedures during the design process to ensure conflicts are minimal.

[Sarcs]

The aircraft used to validate the original procedure was a Navajo, to the best of my knowledge it was not equipped with GPWS.

Pardon my ignorance ac but how can a Navajo not equipped with GPWS, be considered appropriate to certify the approach?

Also, while we're on the subject of GPWS, consider this quote from a pilot statement in the LHR coronial inquest:

Whilst on approach to Bamaga on a number of occasions, Mr ##### observed Mr ####### (as handling pilot) while in a hurry “often pull the circuit breaker on the GPWS”. This occurred when the GPWS sounded a bank angle or high descent rate warning and Mr ####### would de-activate the system, to avoid nuisance warnings, and continue with a visual approach to the airstrip;

(Pg 32 of the coroner's report).
http://www.courts.qld.gov.au/__data/...h-20070817.pdf

I know your all going to say...Rogue pilot, inadequate SOPs etc but if it was known by that pilot that the LHR RW12 GNSS RNAV was known to set off the GPWS while passing over South Pap so he ignored the GPWS. Then I think we have a potentially very big hole in a lump of Swiss cheese!

[waren9]

Agree with alphacentauri

There are some less than informed digs at his posts.There's no such thing as a "nuisance" warning with GPWS, unless then unit itself is faulty, which is another argument altogether.

If a GPWS issues a warning in accordance with its design and that warning is undesirable then the way that the approach is flown for that kind of aircraft and its installation either needs to be modified such that no GPWS warnings are triggered or the approach not flown at all.

Flying your aircraft in such a way as to intentionally trigger a GPWS in IMC is a seriously bad habit.

[Sarcs]

Flying your aircraft in such a way as to intentionally trigger a GPWS in IMC is a seriously bad habit.

waren9 from the ATSB report: http://www.atsb.gov.au/media/1358144/ai2007010.pdf

On 29 May 2007, the crew of a Beechcraft B300
Super Kingair reported that a Lockhart River
Runway 12 RNAV (GNSS) non-precision approach
was being conducted, via the LHRWD waypoint, in
instrument meteorological conditions (IMC), with
the flight management system coupled to the
autopilot:

At a point 5nm from the MAPT [LHRWM] the
Enhanced Ground Proximity and Warning
System (EGPWS)

3 gave aural and visual
alerts of ‘Terrain Terrain Pull Up Pull Up’
which lasted for 1 cycle of approximately 3
seconds. No amber or red terrain indications
appeared on the EGPWS display. At the time
of the warning, the airspeed was 130 KIAS
and a rate of decent of 700 fpm in IMC at an
altitude of 2150 ft. The RADALT indicated
approximately 1600 ft just prior to the event
and decreased to 1000 ft during the event.

The crew responded to the alert, established a
positive rate of climb and conducted a missed
approach. The crew then made a second attempt
via the LHRWG entry waypoint and reported:

During the second approach, in the same
configuration and, at the same position as
the first approach, the same alerts were
produced by the EGPWS.
The terrain map showed only blue and green
terrain and the aircraft was again accurately
on both azimuth and glide path. The flying
pilot noted the RADALT height reduce from
1600' to 1000' over a period of less than 1
second before returning to 1600'. The alert
continued for 1 cycle before ceasing. The
aircraft was confirmed on FMS glide path

and a decision to continue was made…

How can that be intentional activation? I think the last thing the crew of the B300 wanted, was for the GPWS to go off!

[alphacentauri]

Pardon my ignorance ac but how can a Navajo not equipped with GPWS, be considered appropriate to certify the approach?

Because there wasn't a requirement to test GPWS on instrument approaches. There still is no requirement to do this, however the procedures are now flown using a GPWS fitted Conquest.

[waren9]

Sorry Sarcs, I thought this was a thread about a Metro prang and a crew/company that actively flew their aircraft without due regard to the design limitations of the equipment they were using.

[LeadSled]

It was quite common to see errors of approx 75nm suddenly occur during US military ops in the mid-90's.

Folks,
I would have thought it was reasonably common knowledge that the US military (and, I assume, others) have the ability to effectively disable GPS signals over a geographical area.
After all, NOTAMs have been issued when this ability is going to be used, when in US airspace.
I have not seen such a NOTAM for exercises outside US territory, but I would be surprised if this ability was not used during exercises, as the logic is that most large aircraft rely on INS with GPS updates, not just GPS.
If there was a fleet exercise anywhere in the vicinity of the Australian east coast, no way would AU "authorities" ruffle any feathers by even hinting it played any part.
Personally, I don't believe it was an issue, "the" issue was a very unstable approach.
Tootle pip!!

[Frank Arouet]

Metro prang and a crew/company that actively flew their aircraft without due regard

And what Company it was, is still an outstanding question.

Can anybody remember the large signwriting on both sides of the aircraft, what the tickets read, and factor that into who got the blame and paid the penalty?

But that should also be disregarded, as was the fact the US Navy was in the vicinity at the time.

It's just that too many things were dismissed.

[CaptainMidnight]

The US Navy <snip> given that they were near there at the time,

What evidence is there for this? Facts please (name of military exercise underway, or vessel name, or port visited)?

first hand accounts of others who were, I believe that the hypothesis is not without merit.

What were the reports?

I have not seen such a NOTAM for exercises outside US territory,

GPS jamming takes place from time to time and NOTAM issued. If there is an AIP SUPP for a major exercise, it's covered in that also, in addition to NOTAM.

[Oktas8]

I don't think that GPS (in)accuracy had much to do with the catastrophic sequence of events. They were on track after all. Unless you think they were using GPS altitude as the primary height reference. Surely not?

GNSS uses complicated high technology, and the US armed forces are a secretive bunch. This does not logically lead to the conclusion that you are implying.

[Sarcs]

A friend of mine was tasked to a active beacon 200-250nm East of LHR, anyway he homed to the beacon and was initially on top of 8/8ths. When he finally busted through the cloud there was a massive carrier and entourage..i.e. the 7th Fleet!

He made contact with the yanks and they were none to happy he was there...they denied that the beacon was in amongst the fleet and it was subsequently turned off. So he bugged out of there back to Cairns....

[Frank Arouet]

I understand there was another tasked to the LHR site, in fact was first there, who suffered a signal loss around the same time.

They were on track after all

"On track" is three dimensional. It's obvious they weren't on a vertical track.

[InTheWeeds]

I thought they would have been too busy shooting down TWA800...

[thorn bird]

Your mate was lucky not to have a missile up his a...s Sarcs!
busting out over the fleet unannounced, big No No.
No sense of humour the Yanks.
Had them threaten to fire on me unless I got off the airway
I was cleared on.