Trident autothrust system and autoland
 

Watched something on youtube the other day where they were saying the Trident autothrust only applied to nos 1 and 3 engines. Is this normal with all three engine jets and why? During an autoland what happens to the throttle position of the no. 2 engine? Is it manually controlled or locked out so the approach is effectively two engine only? (I can't believe that one!)

Cheers.

No, it most certainly is not.

Was this a misunderstanding that it didn't control the fourth "booster" engine on the Trident 3B ?

Correct, but only for an autoland. For a manual landing, if autothrottle was used, it controlled all three engines.


At around 1,500R, number 2 engine was disconnected from the autothrottle system and manually set at a typical approach RPM, where it remained for the remainder of the approach. For the Trident 3, this figure was 11,200 RPM.

The NHP closed number two throttle manually on main wheel touchdown.


The DC10 and the L1011 did not have this procedure.

As to why the Trident did this, I don't have a definitive answer. Perhaps the designers were concerned about a high RoD building up near the ground if the autothrottle system failed or if it commanded too large a thrust reduction in gusty conditions or if the engines were slow to spool up. Remember the Speys were CTVN engines! Constant Thrust Variable Noise :E

The main reason we did it was.............because it said so in the AOM. ;)

Thanks very much Trident Sim - exactly the answer I was looking for! :ok:

Seems an odd, peculiarly British thing but it worked and paved the way for all autoland systems to follow!

Did the No 2 engine have a significant pitch couple?

It may have been that to avoid the pitch and thrust control loops affecting each other and becoming out of phase, they simply restricted the thrust channel to the 1 & 3 engines, so as to avoid the thrust commands influencing pitch.

Edit: For that matter, did No 2 require any special handling characteristics, or did it come it come on to limits sooner than 1 & 3 (just wondering how well the s-duct was implemented).

Its a VERY long time since I last flew the Trident, but my (hazy) recollection is that number 2 was actually not connected to the autothrottle. The reason was that there was not enough air coming out of an idling engine to keep the aircraft presurised, so on descent, we always had to keep number 2 at a medium thrust level (10,800 N1 or N2 maybe? - too long ago to remember). We never used autothrottle in the cruise, only in the final part of the approach. If the autothrottle was working hard, then number 2 had to be kept stable to avoid ear problems down the back. Rather unusualy, the NHP used to have his hands on the throttles for the approach (in BEA) and, for manual landings, would close number 2 when the HP called for power off. I can't remember what happened for autolands. I also flew the DC-10 later in my career and I was surprised and delighted to find that we could close all throttles at top of descent without loosing presurisation.

I don't remember any significant pitch coupling with centre engine power changes with either aircraft.

The Spey was the same engine as in the One-Eleven, with only two engines. I wonder how they managed then ......

Trident A/T
 

It’s now nearly 30 years since I last flew the “Gripper”, but IIRC A/T was ONLY used for autoland. No 2 was kept mid posn (10,800 O&H mentioned, ‘fraid I can’t remember) for px, UNLESS 1 & 3 were at greater than Reverse Idle, when No 2 could be brought to Idle. (I recorded 22,000fpm during an emergency descent in that config.)
There was no pitch couple (for any engines). I transferred to the B757 after the Trident and that was when I first encountered this phenomenon.
Prober

How surprising, and rather pleasant, that some level of interest in the Trident still exists!


No, not really; certainly not when compared to other, later, aircraft in BA’s fleet. A cynic might say that one needed significant thrust changes to cause a significant pitch change! ;)


That is correct - although it could be if required. It was checked OUT during the pre-take off setting up of the FCS and Radios, and I can't remember No 2 A/T switch ever being engaged thereafter.


Well remembered! I’ve still got the manuals and so was able to look the figures up:

• T1: 10,800
• T2: 11,000
• T3: 11,200

I would respectfully disagree, as my recollection is that A/T was used a lot, perhaps even a majority of the time, on all approaches, during the early days of the Trident fleet, as many a passenger who had the misfortune to sit down the back of the aircraft could probably testify to! The constantly varying noise levels from the engines, as they continually spooled up and down, was appalling!

In the early seventies, many (but not all) older Captains, who had come to the Trident from propeller driven aircraft, were very reluctant to allow manual throttle handling on approach. For those that would permit it, as O & H has already mentioned, it was their hands on the throttles, not yours, a procedure I still think odd!

I seem to remember that it was only after a significant number of Trident F/Os had returned to the fleet as Captains that a more enlightened and sensible approach to throttle handling became prevalent. By the time I flew the T3 in the eighties, manual throttle approaches were very common, and the reduction in noise nuisance, both on the ground and in the cabin, was substantial.

The reason why NHP handled the throttles on approach is that the throttles were so far forward that you could not properly reach them when fully open without leaning forward. This would hardly aid accurate flying.
Just one of the 'gripper's' many design failings.

Trident Autothrottle
 

Many years ago, both the VC10 and Trident had "noisy" autothrottles. At Wisley Flight Test on the VC10 we considerably improved matters by moving the pitot heads further out from the fuselage and out of the boundary layer. As a result of friendly relations between a couple of individuals, we (the VC10 lot) gave the idea for the mod to Hatfield Flight Test free (well, let's say a pint or two) and gratis. Just thought you might like to know this.
Also, you might like to discuss engaging reverse thrust on the Trident before touchdown.

Trident Reverse
 

Ahh - I had forgotten about that. You could actually use reverse at any altitude and so, with full airbrake as well, and despite residual power on number 2 engine, achieve huge rates of descent. The use of reverse in the flair was recommended for very short runways as the brakes were not great. I remember Edinburgh before it got extended and Gibraltar, but, as these were always Captain's landings I never did try it myself. I also happen to know that it often frighten the passengers at the back!

You just couldn't make this stuff up could you!? :p Using thrust reverse at altitude and in the flare!!!!! :ooh: :p

Why was the Trident called the "gripper"? Anything to do with pilots "gripping" the controls in case the autoland system failed or did something unexpected??

Tupolev 154 pinched the idea (maybe the pinched the entire set of blueprints) and have used this for the last 40 years. Plenty of photographs around of doing it.

Allegedly it "Gripped" the ground on takeoff. However, having made more than one departure in those rearward-facing seats it had in the cabin, and felt on rotation that I was nearly falling vertically into the laps of those I was facing (usually the boss) were it not for the seatbelt, I never quite went along with this one.

Quote:

I remember Edinburgh before it got extended and Gibraltar, but, as these were always Captain's landings I never did try it myself. I also happen to know that it often frighten the passengers at the back!


We got used to it at Edinburgh and Aberdeen in those early oilfield days. Gave the SLF something to talk about over a pint in the SKean Dhu. Carrier Deck landings! :p

Trident into Edinburgh :

I recall that the Edinburgh route stayed with the Vanguard until the end of its service, because BA said the old runway was too short, and the wrong orientation for the prevailing wind, to use for Trident operations. This was a significant part of the discussions in the mid-1970s about the new runway.

Once the new runway was approved, it seemed the Vanguards steadily disappeared, and the route became 100% Trident quite some time before the new runway was commissioned (1977 ?).

WHBM: The Trident did do flights into Edinburgh in the early `70`s but I seem to recall that these stopped after a particular Trident slightly overrun the end of 31 into the fence by the Falkirk road. Strong crosswinds at Edinburgh were a problem also for the Vanguard since you could not select Ground Fine until BOTH mainwheels were on the deck and sometimes that was difficult to achieve and so go-arounds off the runway were not unheard of! Still the passengers down the back got a fine view of the runway on approach due to the large drift angle!

The early Trident ones spawned the name "Ground Gripper" as it couldn't take off from Heathrow on a hot summer's day at Max take off weight - it was eventually re engined.
It did go into the old Edinburgh but one ran off the end.

SOP stated that engine 2 had to be left at 10800 even with engines 1 and 2 in reverse in descent although we had a character "batman" who would throttle engine 2 back until the cabin surged during descent into Gib.
He forgot to increase eng 2 rpm when he cancelled the reverse - voila another cabin surge.
He also managed to catch the cabin up with the result at around 3 grand, the dump valve opened and the cabin descended at 1500 fpm - guess the pax loved us!

Manual throttle was not permitted on 3 engines on approach but was compulsory with an engine out!

The most frightening aspect was the short field landing technique, 50 ft throttles off and select white knuckle reverse.

A mate came to a stop with the cockpit hanging over the sea wall in GIB - he was comatose and the skipper pealed his hands off the throttles and cancelled the reverse.

It was the most difficult kite that I flew (six different jets)- min drag was around 225 knots and we approached at approx 135 knots - faster than a lot of other ships which gave problems for ATC with spacing on approach.

I think the NHP operating the throttles came about as a few of the ex bomber command boys found it very difficult to hand fly.
The had all arrived via straight wing piston propellor aircraft.

We did has some excellent older guys but there were a few who thought that the a/p was minimum equipment.

It is probably how the monitored approach system came about.

It changed after with the ex meatbox/hunter and hamble guys arrived in the LHS.

The worst part was dead heading into Glasgow during the winter - scottish ATC wouldn't/couldn't talk to the southern ATC so it was always a dirty dive with reverse/airbrakes and ant icing whilst pointing an mountainous terrain.

The T2 also had a trick where you could drop the main undercarriage (gear in american) at VNE but someone forgot to reset the switch and ex LHR the crew returned as they couldn't raise it.

It was extremely fast and the best fun was racing the Swiss Coronados into heathrow - beat them a couple of times although never managed it into ZRH.

Happy memories!

Her's one to tickle the memory cells.

I seem to remember some Tridents had 2 yaw dampers some had 3. On some versions you could go with one inoperative. I can't remember which way round.

Thank God, I never flew Ground Grippers. Iron Ducks were much better!

Couldn't agree more, loved the iron duck.

Missed one unique gripper feature - the undercarriage oleos had an extremely small movement - supposedly as it was believed that with a normal range of movement that the computers wouldn't be capable of performing an autoland.

There were a few brave souls who had a special landing technique - late flare and at the last moment stuff the stick fwd.

It worked wonders and used the technique later on the DC9-51 which was also difficult to grease on at 300M with a normal flare.(the earlier 9s weren't a problem).

If you manage to get hold of a copy of the corporations recruiting film made in the mid 60s you will see both the Gripper and the Duck.

Most entertaining - and enlightening-but showed a typical trident controlled crash.
It is available through the Hamble web site!

Memory tricks
 

Indeed, one does forget! Yes, of course the A/T was used for most approaches as well as A/Land - not as I said earlier. Yes, there was a switch somewhere in the ceiling for engaging No2, but this was, to my knowledge, never used. And reverse was selected at the flair for all landings so far as I recall, with the final few seconds spent floating on a cushion of air. The main gear as an airbrake switch actually disconnected the nose wheel deployment and the incident mentioned suffered a "nose wheel fails to lower" when it came to the actual landing. The switch was then disconnected! I remember more difficulty at Gib on the Vanguard rather than the Trident, with the fire service knocking on the window at the end of one white knuckle arrival! The worst of that airfield was the (RAF) controllers telling you that you had just violated the other side's airspace, rather than telling you that you were about to and you could then have done something about it. Hey Ho! As to EDI, T1 and T2 ops were usually uneventful (on 13/31). The arrival of the T3 caused tire bursts on a regular basis, and the previously mentioned method of touchdown (nose forward), was developed by some intrepid pilots and it worked very well, but trg establishment would rap our knuckles. It was a delight to fly and I enjoyed most of my 7,000 odd hours both as P1 and P2/3.
Prober

Ok, Ok, I know the Gripper, but what's an 'Iron Duck' and why??

WHBM asks about how BC 111 got on with two engines
 

Sure, the BAC 1-11 used only two Speys against the Tridents three, but it only weighed about two thirds the weight of the Trident 3 at MTOW.

You could do it on many aircraft of the era.

Ergonomics weren't a big thing on any airliner back then, no matter who made them! Early 707s were famous for having slightly different cockpit layouts depending on the customer.

Technologically speaking the Trident was probably the most advanced airliner in service at the time it was launched - most of the compromises that hobbled it were in fact demanded by BEA. This is borne out by the fact that Boeing took the original specification and design (minus the advanced avionics) and copied it almost verbatim in the form of the 727, which went on to become the best-selling aircraft in the world, holding the record for nearly two decades.

If only BEA hadn't meddled and Trident got the RR Medway engine originally specifed...

Ths is a long-standing comment, but I wonder how accurate it is, apart from the basic aircraft configuration. The 727 front end and fuselage were taken directly from the 707 (and the 737 still is). Is the DC8 also a 707 copy, because it was the same configuration ?

As I understand it, although the first Trident design had more substantial engines, it didn't have the high-lift devices of the 727 which lifted the first 727s off short runways because it was intended (by BEA) to operate from Heathrow to other major European airports, most of which were already handling 707s etc, whereas the 727 sold initially to US airlines to operate into many places where the DC6 was the biggest they had seen up to then. I doubt either Trident version could have operated out of the 6,000 foot runways that La Guardia had when the 727 came into service.

The first generation of "smaller" jets, 2 and 3 engined (of which the pioneer was the Caravelle), all went for rear-end, fuselage-mounted engnes, because that was more straightforward to control with an engine out, plus they were concerned about sucking up FOD on lesser runways. Only when the 737 came along had the research been fully done on how to handle wing-mounted engines. This configuration then came back into vogue more recently when all the the RJs came along, for different reasons which we need not dilute this discussion of the Trident era with.

twochai

The Iron Duck was the magnificent Vickers VC10. Our irreverent colleagues on 707s used to call it that because much of the structure was milled out of the solid - alumnium not iron! I spent many happy years flying VC10s.

Interesting article here - no proof of course, but it does seem an odd coincidence:

British Airliners 'Nearly Get It Right' Shock! - Aircraft of World War II - Warbird Forums

You're right in that the Trident didn't have the same high-lift devices as the 727, but the first generation's droop and flap configuration was still pretty potent. It needed to be, because the wing was designed for high-speed cruise (I have it on good authority that despite being a bugger to get off the ground, the Gripper went like a scalded cat in cruise). Re-use of the 707's nose and fuselage section would always have been a no-brainer for Boeing, because they already had all the jigs and tooling in place.

While you're also right about the Caravelle, the Trident was the first design to use a triple engine configuration with an S-duct on number 2, which is the primary similarity with the 727. Had it had the Medway engine as specified, I don't think it would have found a 6,000 ft runway a problem. Purely speculation though. :)

IIRC the title sequence for the BBC series "Softly Softly Task Force" showed a BEA trident landing at GIB and you could see the reverse thrust smoke from the cascades before touchdown.

Main gear as airbrake event
 

Prober, "The main gear as an airbrake switch actually disconnected the nose wheel deployment and the incident mentioned suffered a "nose wheel fails to lower" when it came to the actual landing. The switch was then disconnected!!" ...... not quite the full story......... "I was that man"!! (Also can you point me to the post with the "incident mentioned").

We were doing LHR-GVA-LHR in about 1967 (EDIT: 16 December 1966) in a Trident 1 (EDIT: GARPM) , with a Very Senior Management Pilot (VSMP) in the LHS making his once a month recency flight, and as I recall he flew the approach. I was the junior F/O with one ring I think. Can't remember the SFO in the RHS at the moment (EDIT: SFO Chris Cross) and my logbooks aren't to hand. Strong NW tailwind and held up very high by French ATC all the way to the then Swiss border, as was their habit, before getting clearance to descend from GVA control. Anyway the very late TOD meant using everything to get down expeditiously approaching.

IIRC the layout was that the airbrake lever was on the left side of the console, and just to one side and behind its stowed position was a toggle switch which enabled you to drop the main gear only, as you said, at a max. speed of 320 kts (?) IAS. Alongside the switch was an amber warning light to tell you you'd used it. Retraction was limited to 280 (?) though.

VSMP deployed airbrake lever and then main gear while decelerating, cleaning up as the speed decreased and we got round and landed with no problems.

We turned around and took off again, and on selecting gear up the main wheels stayed firmly down: 2 reds and 2 greens. The main gear had an emergency free fall that was activated via a hatch in the centre cabin floor that actually opened into the cargo hold, and accessed a lever for a compressed air bottle that would blow the gear down.

VSMP says there has been an incident elsewhere on the network where a loader in the hold has grabbed this lever and discharged the bottle, causing the main gear to refuse to retract. Therefore that is what has happened. Declares an immediate return to GVA and we went back and landed. VSMP departs cockpit to investigate and deliver bollocking to ground staff.

SFO and I are discussing this in this his absence and doing the turnround checklist when we notice main gear airbrake switch is still in "extended" position although the warning light is out.

VSMP returns and red faces ensue. SFO and I got an informal bollocking from chief pilot for not being smart enough to know that VSMP needed watching like a hawk! and "lessons are duly learned".

Meanwhile VSMP takes up subject of failed warning lamps etc. with manufacturer (de Haviland). It transpired that on every other aircraft on the fleet there was a striker pin on the airbrake lever, such that when the airbrake was stowed after use, it would also return the "main gear airbrake" switch to the "up" position, if it hadn't already been done. It wasn't installed on this aircraft! More significantly, they were horrified to find that we were using this facility on a relatively routine basis, as it was only intended as an emergency facility for rapid decompressions etc. Hence came the removal of the ability to use it - I can't even remember if it was even actually installed on the T2 and T3.

Happy days!
Steve

As pointed out Vickers built the VC10 and supposedly used ship building techniques - I was told that the Iron duck came from the substantial titanium brackets that held the donks on!

Trident gear/airbrake limits. Lower retraction speed was if the grey matter is correct - due to the nose gear doors ( undercart was off set with one large door).
The main gear airbrake was still in use in 1972 when I come onto the gripper - I believe there was yet another incident at lhr before the function was inhibited.

Cruise speed - yes it was very fast but MMO had been reduced (think it was originally M.92)
It went very fast on one special flight with a couple of Very senior management extremely competent pilots (if you believed them) who,if P3 is to believed, pulled the CB and flew at M.design as tghe young lady down the back was late.
I think most of us heard about it as P3 made a point of telling all and sundry.

Noise
 

Can you expand on this idea of controlling noise? I can only think you are saying the centre engine was disconnected to cut down the noise when the autothrottle applied full power. This would suggest it was inclined to command wide power excursions. Was this an accepted shortcoming? Did leaving the centre engine at a fixed power mean the aircraft took longer to regain the glidepath?

I think it was to reduce the degree of noise changes inside the rear cabin - as the centre engine was in the rear fuselage it was pretty noticeable.

n/gear
 

Marvellous after all these years to hear from the horse's mouth. Unlike Chinese Whispers, the story actually did not get too twisted in the telling, but it is wonderful to hear what actually happened. Thanks, Steve for that.
Fast? Yes it was. Normal cruise was M.88 (on the T1). (I recall a charter from SNN to VIE in which we managed an average of 660 kts G/S - but not quite the same on the way back!) M.92 was the max during base training and recovery from that proved just as frightening an experience as deploying airbrake on the T7 Hunter at M1.1, or landing an Auster on a carrier. The T2 was .8 for no other reason than IIRC wear and tear. Then came the 1974 fuel crisis which, apart from producing the national speed limit of 70 mph (it was nothing to do with road safety), made everyone thing seriously about fuel. Up till then, fuel was not much more than an incidental in one's costings and consequently the cruise speed for all Tridents was reduced to M.8 or maybe .78 (I cannot remember).
As to noise, the Gripper was far preferable to the B1-11 with A/T engaged. The 1-11 had to do it all with 2 engines whilst the Gripper had the modifying influence of the steady No 2. Positioning on the 1-11 was not a pleasant experience, especially down the back.
Prober (Mike)

The 70mph national speed limit was first introduced as a temporary measure in 1965, and made permanent in 1967. The 1974 fuel crisis lead to a 60mph limit on dual carriageways, and 50mph on all other roads except motorways, where the 70mph limit still applied.

Anyway, please forgive the digression, and many thanks for all the Trident stuff.

Do you mean this film?

You can at one point clearly see the Throttle's 1&3 moving with 2 being in the roughly 12 o'clock position.
Wanted to post the same question about the auto throttle when I first saw these movies, but forgot.
Thank you everybody for the great stories...Really like the trident:ok:

Good night

Micky

Ps Really like the kick off drift writing in the RA...

What a great fim! I love the bit with the test pilot nonchalantly talking to the camera over his shoulder as the aircraft descends through two hundred feet. Talk about confidence in the autoland system.

Forty years later I am not sure how much things have improved. I certainly would not feel comfortable doing that on my 737....not after the autopilots tripped out in the flare a few weeks ago! Certainly got my attention.

Hi Prober,
I'll have to dig out the old logbook I guess, Blindpew says we were still using main gear airbrake in '72 so it looks like I may have compressed the timescale from our event to it eventually being removed as a facility. As a junior F/O I wasn't privy to any of the management discussions! I seem to remember it was Peter Harper, with whom I later worked a lot on BALPA's technical committee, who said DH weren't happy about it, but it's a bit hazy in the mists of time!!

A/LAND - No ILS!
 

All this reminiscing brings another snippet to mind. As F/O I went to FBU with Capt Ormonroyd (Snr) who was one of the A/Land boffins and aces. FBU closed, so we had to go to Gardemoen which, in those days, was a minor satellite, semi mil, used for diversions (by BEA). We were given an NDB Approach and Capt O said that now we had a chance to prove the A/Land system. We two minions looked at each other slightly aghast, but Capt O just asked us to cast our minds back to how the system worked. All very well for him - he was a semi boffin - but we were mystified. "Remember", he said "at 133ft the aircraft system disengages from the ILS and flies the final bit on memory. We will fly a steady approach and fool it into thinking it was doing an ILS!"
We held our breath and after touchdown (hands off - nearly) I swear he smirked.