Tridents and the Autoland system
 

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

1) What were the autoland limits?

2) What was the actual weather?

If 2 is less than 1 you divert.

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

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.

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??

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.

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).

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.

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

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.

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!

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)....

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.

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.

<<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?

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.

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 . They're running a thread on Blackbushe piccies from the past, many from the Bennet era but mostly before.

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.

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.

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.