Tridents and the Autoland system

[MARK9263]

Something that has always intrigued me. If all Tridents were fitted with the Autoland system, then why, would there be any need for an aircraft to divert away from Heathrow due to visibility?
Having been researching movements at Manchester during the 1970s, there were still plenty of Trident flights diverting from London due to fog.

Could one reason be that the crew were not trained to 'land' on Autoland?

I would appreciate any further assistance on this baffling matter!
Many thanks
Mark

[BOAC]

1) What were the autoland limits?

2) What was the actual weather?

If 2 is less than 1 you divert.

[MARK9263]

I thought the whole point of Autoland was that it landed the aircraft irrespective of the vis,rvr or cloud base?

[Groundloop]

A quick look on Wikipedia (so may not be accurate:ok:) gives the following:-


"The first aircraft to be certified to CAT III standards, on 28 December 1968,[1] was the Sud Aviation Caravelle, followed by the Hawker-Siddeley HS.121 Trident in May 1972 (CAT IIIA) and to CAT IIIB during 1975. The Trident had been certified to CAT II on 7 February 1968."

Therefore there could still be many diversions in the 70s if the vis was below the then current certified limits.

[MARK9263]

Many thanks for that...

After 1975 when the type was certified IIIA, generally it was possible to land in an RVR of 75m.

But still by 1978 there were still Tridents flights diverting away, possibly by Heathrow not accepting any flights whatsoever at that point in time, or the crew not certified as the 75M RVR was such an extremely rare event??

[ICM]

Landing in very poor vis is/was not the end of the matter. Airport authorities presumably then need to have some assurance that aircraft can navigate to a gate without accident? Just a thought.

[Aileron Drag]

Everything had to be working in order to be Cat 3. Often, an aircraft would be Cat 2 only, or even Cat 1 only, due to a u/s component.

You couldn't guarantee that every Trident would be Cat 3 capable on every day.

Even then, if the skipper didn't quite see the lights at 12R, the P2 would immediately go-around, and in later years consideration for the passengers' nerves would preclude more than two attempts (think Double-Echo accident).

[Jhieminga]

Another thing is airfield capacity. With CAT III weather the number of aircraft that can land per hour goes down dramatically. The Tridents concerned may not have had enough fuel on board to await their turn in the queue, another good reason for a diversion.

[ajd1]

And we didn't have Autoland on the 1E.

[ICM]

Incidental to all this, does anyone know to what degree, in financial or just operational terms, the cost of developing the Smiths system was amortised (or hidden) by the lengthy work done at RAE Bedford with the RAF's Short Belfast, XR364? As I recall, the aircraft did about 4 years or so up there before finally reaching 53 Squadron at Brize Norton - and the great irony was that the RAF never got an autoland capability from it at all.

[chevvron]

On my first ride in Comet XV814 from Farnborough, the Captain, Ken Mills, indicated the some items on the centre console and told me that it was the prototype of the Trident system.
On my ATCO's 'How to fly a Trident in 2 weeks' course, I'm sure were were taught it was the captain's job to land the aircraft and the FO's job to go around, hence at 12 ft radio, the FO would call 'decide' and if the captain did not reply, the FO would advance the thrust levers thereby initiating the automatic go-around system. On the systems trainer we used, it was very sensitive and only needed the slightest touch for the thrust levers to slam forward!

[G&T ice n slice]

Wasn't the system installed so accurate that they had to have the nosewheel gear offset from centreline, because otherwise the wheels would go banging over all the runway centre-lights, jarring the crew (and pax)....

[Aileron Drag]

G & T, that's an old wives' tale! It was true that the Trident would go-around from 12R without touching the tarmac, being well into the flare.

P2 was, as it were, determined to go-around. The slightest hesitation on the part of P1 to say "Land" would result in a GA.

Good point from Jhieminga about the airfield, and the queue!

The Trident A/L system was absolutely brilliant. On one memorable day (a double shuttle), it was on-limits at both ends, and we took-off and landed - four sectors - on schedule and with no trouble. We were also one of about two aircraft in the air that day!

Brilliant technology.

[Allan Lupton]

Hadn't heard the myth of the reason for the offset nose gear before!
Back to the "why divert" question with a couple of points:
You'd divert if the taxi-in in Cat 3B would be too dodgy (as ICM has said).
Take-off in 3B wasn't popular so the airports filled up, so ran out of ramp space.

[HEATHROW DIRECTOR]

<<Landing in very poor vis is/was not the end of the matter. Airport authorities presumably then need to have some assurance that aircraft can navigate to a gate without accident? Just a thought.>>

Where I worked there was ground radar and controllers had to display their ability to navigate aircraft around the airfield before they validated. There were regular exercises using AFS vehicles during night watches where the fire vehicle would have the windscreen covered so the driver depended entirely on ATC for guidance. I excelled myself by steering one such vehicle into a pair of engineering steps which were not showing on the radar! Wonder if they still happen?

[srobarts]

I remember as an SLF on the shuttle in the early 80s, arriving at LHR Carpark 1 where all you could hear was the creak of the radar going round. Once boarded we had the captain's intro telling us that the plane might be equipped with all the fancy technology to take-off and land in the fog, but it didn't help them find the runway! So we waited for the fog to lift enough to taxi.

[chevvron]

HD: although I never worked in the tower at Heathrow, you did hear tales of these fire service runs, like the one where there was a slight 'shadow', the controller took the fire truck through it not knowing it was cordoned off with a line of oil drums which ended up scattered all over the place.
Oh by the way, take a look at Farnborough-aviation-group (http://www.Farnborough-Aviation-Group.co.uk) . They're running a thread on Blackbushe piccies from the past, many from the Bennet era but mostly before.

[Tagron]

In the 1970s very few aircraft types and operators using LHR were Cat 3 capable, and even fewer could operate to Cat 3B. This meant that in stabilised Cat 3 conditions a suitably equipped and qualified aircraft and crew could usually expect no delay for the approach, because for the other operators RVR was below limits, and many shorthaul flights would have been delayed or cancelled. That is a far cry from the present situation where the majority of aircraft will be Cat 3B capable and the reduced inbound flow rates are controlled by departure slot restrictions at European airports.

That advantage would not have applied in a deteriorating or fluctuating weather situation. Then the Cat3B aircraft would have to take its turn, with the risk of needing to divert due to insufficient holding fuel. So this could be one cause of Trident diversions.

The other issue would have been aircraft certification and serviceability. Certification to full Cat 3B was progressive. Then various equipment defects on the day could result in autoland capability downgrade. On the L1011 (and here I will admit to not having been a Trident operator, but the the L1011 drew heavily on Trident AWOPS experience) nuisance warnings or genuine unserviceabilities could leave a nominally Cat 3B aircraft only usable to Cat 3A or Cat 2..

To put some numbers on these categories. Cat 3A minimum RVR was usually 200m.. LHR RVRs were often below that figure in fog conditions. Down to 150m was common and just once I saw 125m. I never heard of 75m RVR at LHR nor did I hear of captains declining to taxi in those conditions, but then that does not mean it did not happen.. The 75m RVR requirement was to ensure some sort of minimal visibility for vacating the runway, and for the emergency services to find the aircraft if required. Technically the RVR could have been zero, after all zero decision heights were approved, though this was for the L1011 and my knowledge does not include the Trident.

[Aileron Drag]

Regarding finding your way to the runway, we had low-vis pages in the aerodrome booklet for LHR showing the magnetic direction and distance of each section of the route to the runway. The distance was set on the Ground Run Monitor at, say, the start point at the end of the Bravo cul-de-sac.

The GRM would be reset at the threshold to the TOR, so you'd know how much runway you had remaining in the event of a rejected take-off.

This was used as a crew 'check' on the Ground Controller's instructions using their Ground Movement Radar (was it called 'ASDIR'?). Not that we didn't trust them, you understand. :)

I never heard of a crew unable to taxi out, even in 3B. The combo of ATC radar and the GRM/chart usage worked like a dream.

[srobarts]

I never heard of a crew unable to taxi out, even in 3B. Thanks for the feedback, it was on just one occasion, so maybe it was a tech problem and the captain wanted to make light hearted announcement because of the delay. So many of the SLF on the first flight of the day seemed to get really irritated by any delay.

[spekesoftly]

Ground Controller's instructions using their Ground Movement Radar (was it called 'ASDIR'?).ASMI - Airfield Surface Movement Indicator.

The Decca Legacy - Chapter 6 (http://www.woottonbridgeiow.org.uk/decca-legacy/chapter6.php#6.1)

[chevvron]

Or its successor ASDE (Airport Surface Detection Equipment)

[HEATHROW DIRECTOR]

<<I never heard of 75m RVR at LHR >>

Guess you never worked at Heathrow? Not only have I seen RVR of 75m, I have also seen 000 on a number of occasions.

T.. Thanks for the tip; I'm following PBs pics on the Farnborough group.

[Tagron]

Actually I worked at Heathrow or to put it more accurately out of Heathrow for more than thirty years. It would be fair comment of course that anyone on the spot in ATC every day would have a more comprehensive view than mine. Even so I would call 75m RVR (as opposed to met visibility) a rare event - middle of the night perhaps ? Below 75m RVR would have stopped operations for everyone and I don't recall that myself.

[JW411]

Please forgive me if I have said this before but the Smiths Autoland system as fitted to the Trident (which I never flew) and the Belfast (which I certainly did) was a very fine system and it was very accurate. It was, however, very complicated and relied on a Triplex system which worked on the principle that if any one single item failed during an autoland, then the other two systems would vote the troublemaker out of the logic and continue to a good resolution.

The big problem was that to achieve this (at the time) amazing result, the amount of equipment required to be carried was vast. the aircraft had to carry, for example, three VRUs (Vertical Reference Units), three RGUs (Rate Gyro Units), three Auto Pilots, three ILS and GS receivers and three bits of wire to every control surface.

I seem to remember that the whole lot weighed about 1,700 lbs which had to be be carried around whether you needed it or not.

All of this came before the invention of PCs, Microprocessors and the mobile phone.

Nothing that happens nowadays achieves a better result when it comes to landing in fog but I doubt that the modern equivalent weighs more than 100 lbs to achieve the same result, but it was all quite exciting at the time.

[HEATHROW DIRECTOR]

Tagron. Yes, stopped it for just about everyone except an RAF VC10 which had brought in a VIP earlier. When asked his minima for take-off he replied "I do not have a minima"... so take-off he did!!

We used to get nervous in poor vis that the oncoming watch might not make it so we used to wind the ASMI out and watch if there was traffic on the M4.

We must have spoken many times. I started at Heathrow in Jan 1972 and retired in Nov 2002.

[Tagron]

HD, My dates were fairly similar, September 1969 to December 1999, so yes we must have had numerous conversations.

[G&T ice n slice]

G & T, that's an old wives' tale!

Hadn't heard the myth of the reason for the offset nose gear before!

Of course the other O.W.T. is that the things only ever got airborne because of the curvature of the earth....(just in case you hadn't heard them called that)

HS Trident a.k.a. the HS Ground-Gripper. forward thrust provided by 3 noise generators, soundwaves thrusting the aircraft forward - More speed? turn up the volume....

Talking about fog at LHR, once after finishing a late shift on the south side missed the last bus & had to walk home, in the fog. Damned nearly walked into the outer waterway at the crossing by Stanwell, where there were no street lights, pitch black and 000 visibilty.

[windowjob]

Chevvron, the "tales of fire service vehicles being led into oil drums" were true - I managed it one night! The sound in the background of drums being hit as the man in the cab was talking on the R/T was something else.

There were specific taxy routes for Tridents from the cul de sacs and as said they stopped at the stop bar at the exit to set the GRM so they knew where they were as they groped their way along the green taxiway lights (set at max brilliance) Also there were makings to indicate curves coming up.

It wasn't just that the aircraft that were CAT III, but the crew had to be current as well. With 3 crew it wasn't unusual for them to hold in order for P2 & P3 to swap seats so they were legal.

I remember the day early on in LVP's when we had very low vis and ran a sweepstake to see what time the first a/c would land. Some hours later it was won. Only weeks later, we heard the pilot was being investigated for landing below limits and asking for our help! Problem was "finger trouble" when he was recorded as landing on the other Runway in the log.

We could prove he was OK as we all remembered the amount of money the lucky sod won!

[blind pew]

Last aircraft out of heathrow one night before it closed as RVR was falling below take off minima. We had twenty odd miles viz over a sea of fog which just covered the transmissometers.
Surreal.
Next company had a "look and see" policy (if we suspected any anomalies in the reporting system) which got us into egkk after it had officially closed - egll had an approach ban due viz.

[Centaurus]

P2 was, as it were, determined to go-around. The slightest hesitation on the part of P1 to say "Land" would result in a GA.


That sounds awfully scary with a transfer of command from the captain to the F/O at flare level and on instruments too. Did the F/O say "I have control" before he pushed open the throttles without telling the captain what he intended to do? Or did the captain just accept the F/O could do a better job of a GA than he? In those days were the F/O's low hour cadets?

[chevvron]

Tridents (BEA ones anyway) always carried 3 crew ie Captain and two FOs, although the non-flying FO was I believe, referred to as second officer. They swopped places on consecutive sectors.

[JW411]

I think most operators in this part of the world operate the monitored approach system in bad weather.

The first officer is programmed to fly the approach (using the automatics) to decision height with the intention of making a go-around.

The captain monitors the approach and is programmed to land the aircraft provided that sufficient visual reference is available at minima.

It works very well. The first officer calls "Decide" at minimums.

The captain will either call "Land" in which case he takes control and lands. The first officer simply takes his hands and feet off everything. Nothing needs to be said by him.

Otherwise, the captain calls "Go Around" whereupon the first officer immediately carries out a go around and the captain monitors his actions.

It gets rid of the bad old days where captains were flying the approach AND trying to look up at minimums and land while the first officer was sat on his backside doing very little.

[DaveReidUK]

The first officer is programmed to fly the approachSorry, but that's carrying automation one step too far.

http://www.travelsnitch.org/wp-content/uploads/2010/10/TS_airplane_autopilot.jpg

[BOAC]

Yet another co-pilot with an over-inflated ego..........

[Aileron Drag]

I think Centaurus has misunderstood the SOPs. As JW411 has indicated, P2 flew the entire approach, with the firm intention of going around at DH, unless P1 said "Land" in response to P3's call "Decide".

There was no transfer of control during a missed approach.

If P1 called "Land" at DH, P2 would simply let go of the controls and be prepared to select reverse and lift-dumpers. If P1 said "Go-around", or said nothing - P2 would go-around.

[Fareastdriver]

The first officer calls "Decide" at minimums.

If you are P2 with a hot date that night you call d..e..c..i..d..e...

[safetypee]

As above from JW and AD, the procedure was simple and safe. The variant which I recall had ‘Decide’ at 15 ft above DH with either a ‘Land’ or a ‘GA’ response before DH (~2 sec later). With the latter the PF pressed GA for an automatic GA. In both instances the Captain continued monitoring.
The ‘wags’ view of having no response – default to GA, was (no response) “the Captain is dead – long live the new Captain” – ‘Land’. In reality this was an accepted procedure to cover the rare circumstance of an incapacitated Captain, thus the autoland option was the safest course of action.

During research flying which investigated the limitations of human capability in fog - auto disengagement or manual take over, the procedure was modified to include the Captain tapping the hand of the PF. This confirmed the decision to land and overcame intercom blocking if the visual scene / workload was being described.

[DozyWannabe]

The big problem was that to achieve this (at the time) amazing result, the amount of equipment required to be carried was vast. the aircraft had to carry, for example, three VRUs (Vertical Reference Units), three RGUs (Rate Gyro Units), three Auto Pilots, three ILS and GS receivers and three bits of wire to every control surface.

Indeed, and if my memory doesn't fail me it was this shedload of avionics equipment that was the reason for the transverse-mounted offset nose gear, because there was no other way to squeeze it in!

[sevenstrokeroll]

FWIW...many years ago, when black and white TV was in fashion there was a TV show in the USA called: THE TWENTIETH CENTURY...it was on CBS. Either Mike Wallace or Walter Cronkite was in the cockpit of the trident as it made an autoland, the captain looking backwards at the Camera explaining what was going on.

It might be of interest to you all to see it...of course I don't know if it is available today. It made quite an impression on me back then.

[DozyWannabe]

Haven't seen that one, but there are a couple linked in this thread from a few months back:
http://www.pprune.org/aviation-history-nostalgia/502878-trident-farnborough.html

[BOAC]

I also recall some even older RAE film taken from a Varsity as it rumbled out of the fog for an autoland with a digital radalt bottom right going "50 -40 30-20"... - look there's a runway!!.

[Allan Lupton]

Quote (how can one do this properly without any "quote" buttons showing?)
FWIW...many years ago, when black and white TV was in fashion there was a TV show in the USA called: THE TWENTIETH CENTURY...it was on CBS. Either Mike Wallace or Walter Cronkite was in the cockpit of the trident as it made an autoland, the captain looking backwards at the Camera explaining what was going on.

Not sure about anything shown in the US, but there was a film made by the de Havilland film crew of a Trident autoland which featured Jimmy Phillips in the captain's seat with his back to the approaching runway, explaining to the camera what was happening.

[Wander00]

Ref BOAC's post I well remember being surprised to be stopped by the traffic lights on the A15 at Waddington on a very foggy evening in 1964 or 65, and even more surprised to see a Varsity lumber out of the murk and land - until we saw the Blind Landing Experimental Unit titling. Well impressed.

[chevvron]

This would have been the Bedford based BLEU Varsity which operated from about '62.