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.