Dredge Bridges - Lochy Bridge and Bridge of Oich

Today, I came across the picture above of the road bridge across the River Lochy at Fort William, the one which carries the 'Road to the Isles' (A830) west to Mallaig. It's not the present bridge, obviously, but I sort of had it in my mind that the previous bridge here had been a suspension bridge. There was nothing for it: I had to research the history of the bridges at this spot. So here it is in reverse order.

The present bridge was built in 1968 and replaced the one pictured above. It was built in 1928, designed by Sir Owen Williams. I'd heard that name before and thought it might have been him who designed the two distinctive bow shaped bridges from the same era on Rannoch Moor (you know - these ones). But according to this article these weren't actually by Williams although he was responsible for a number of road bridges in Scotland, mostly on the A9 and mostly now by-passed (see here).

The 1928 Lochy Bridge replaced a suspension bridge built in 1849 pictured below: this was the first bridge across the river here and, as you can see, its towers were retained in the second, 1928 bridge (although just for decoration as the deck of the 1928 bridge was supported by piers on the riverbed rather than suspended from wires running between the towers).

Lochy Bridge 1849-1928 looking west. Picture credit Aberdeen University Archive

Now I called the 1849 bridge a suspension bridge but strictly speaking it's not, it's a taper suspension bridge. According to the Wikipedia entry for them, they:

differ from the conventional suspension bridge design in that they effectively function as a double cantilever bridge. Each opposing cantilever system is self-supporting. The cantilever half-deck structure of each cantilever is suspended from angled chains, which hang from a tapered main attached to the top of the tower and to the outer end of the half-deck. The main chain taper is achieved by incrementally reducing the number of links stacked across the chain's width as it moves farther from the support tower.

No, I don't understand that either. Maybe it just means it's sort of half cantilever (like the Forth Bridge) and half suspension? Anyway, taper suspension bridges were also called Dredge bridges after their inventor James Dredge who patented the idea in 1836. Their advantage was that they were cheaper and quicker to build. Lochy Bridge cost £1,790 (about £200,000 in today's money), paid for by the local landowner Cameron of Lochiel. That was considerably cheaper than the lowest offer received to build a traditional stone bridge which was £8,000 (about £900k today). The Dredge bridge also took just five months (August to December 1849) to build.

Although a road had been built from Fort William to Arisaig by the Highland Roads and Bridges Commission in 1805-1808, no bridge over the River Lochy was provided at that time and travellers had to continue to use a ferry across the river. A newspaper report of the building of the 1849 Dredge bridge to replace it referred to the ferry as "well and attentively managed" but nevertheless a "plague of careful shepherds and a cause of dread to nervous travellers".

To anyone who has had occasion to cross the river in the old ferry-boat, even in a calm fine dry day, it was unnecessary to say that there was loss of time and much inconvenience experienced; but in a dark wet Lochaber night how very much were all the disagreeables of the ferry increased? The ferry has this day given place to the bridge, and Lochiel has thereby conferred, not on his tenantry merely, but on the public at large an important boon.    

So said Sheriff Fraser at a dinner to celebrate the opening of the bridge held at Robertson's Hotel at Banavie on 20 December 1849. Sadly, Lochiel's health prevented him from being there but James Dredge was: he had supervised the work personally and the sheriff praised him for having paid for cakes and oranges for the 400 local schoolchildren who had turned out on opening day.

But wait a minute - was Lochiel actually as generous as he'd been cracked up to be? The 1875 Ordnance Survey 6 inch map (below) shows a toll gate on the bridge. Does that mean Lochiel had merely fronted the price of the bridge but was expecting to get it back from his dutiful tenants and shepherds over time through tolls? I don't know but no toll gate is marked on the 2nd edition of the 6 inch map surveyed in 1899 (here) so perhaps the price had been paid off by then.

National Libraries of Scotland 

 

There's nothing left to see of the Dredge bridge at Inverlochy but you can still see another one not far away. It's at Bridge of Oich where the A82 crosses the River Oich as it debouches from Loch Oich at Aberchalder just north of Invergarry.

Bridge of Oich from the east. Picture credit: Shawn With the pediments above the arches, I wonder if Dredge was consciously evoking the Georgian architecture of nearby Fort Augustus in contrast to the medieval architecture of Inverlochy Castle he'd sought to evoke with the decorative battlements on the towers at Lochy Bridge?

The Bridge of Oich was built a year after Lochy Bridge, in 1850 (not 1854 as its Historic Scotland and Wikipedia entries say). It replaced a traditional stone bridge which had been washed away in a storm in 1849. (The same storm carried away half of the bridge over the River Oich at Fort Augustus, the rest of which is still standing today (see here), and the whole of the 17th century seven arch bridge across the River Ness at Inverness (see here)). The Bridge of Oich took three months to complete and cost just £620 although it was much shorter than the Lochy Bridge (145 feet (45 metres) as against 240 feet (75m)). Dredge had also stipulated that he would be able to use free of charge the stone from the fallen Bridge of Oich his was to replace.

Dredge also gave a two year guarantee on the Bridge of Oich meaning he would rebuild it at his own cost if it was damaged from any cause within that period except lightning, earthquake or civil commotion. I'm not sure if he gave a similar guarantee at Inverlochy but it was brave of him to do so at Aberchalder because three bridges at this spot had been washed away by floods in the last 35 years. And it's a testament to Dredge's design and workmanship that his guarantee was never called upon and the Bridge of Oich is still standing today. It was bypassed by a new road bridge 100 metres up stream in 1932 (see here and here) but was left as a footbridge. By the 1990s it had fallen into disrepair but was restored by Historic Scotland in 1995-97 and today is a Category A listed building. You can go for a virtual walk across it here.

I leave you with a photo of an interpretation board at Bridge of Oich explaining the Dredge design. (It looks far more cantilever than suspension to me but what do I know ...?)

This board also has the error that the bridge was opened in 1854 but contemporary news reports are quite clear that it was built and opened in 1850. Picture credit Adam Fagen

 

The Korean plane crash

This has got nothing to do with Kyles or Western Isles but it’s another subject I’m interested in and I found myself writing this to try and make sense of it in my own mind so I’ll just publish it here anyway.

So, video of the plane on its original final approach shows a puff of smoke and flame from the RIGHT engine consistent with bird strike.

Moments later the pilot tells control:  “Mayday, Mayday, Mayday, bird strike, bird strike, going around”

First thing puzzling the YouTuber 737 captains (Dennis is very good) is: why did they decide to go around (overshoot the runway) instead of continuing to land?

Second puzzle is that a bird strike, even one which wrecks an engine, is a not a Mayday because a 737 is perfectly capable of flying on one engine so there’s no immediate danger.

One minute later, the pilot tells control he’s going to land on the same runway from the other end, do a U-turn, in other words. The experts will tell you that’s a very bad idea, unless absolutely necessary, due to the risk of making an arse of it by doing things in a hurry.

The decision to do a U-turn suggests that, in fact, the plane had lost BOTH engines and therefore going the long way round to land in the original direction wasn’t an option.

This is corroborated by the fact that the experts are saying that you can see from the landing video that the LEFT engine appears not to have been running when it landed (no exhaust visible) whereas the RIGHT one (the one the earlier video showed emitting a puff of smoke and flame) appeared to be running (visible exhaust) although we can’t tell how much thrust it was delivering – maybe not much at all.

The second (left) engine might have been lost from a subsequent bird strike not caught on camera. Or it might be that the pilots misidentified the engine which had been hit and shut down the good engine (that’s happened before – British Midland at Kegworth (East Midlands) in 1988.)

Kegworth 1988 - didn't reach the runway and hit motorway embankment. Lucky not to burst into flames

And we know that the plane landed with its flaps and wheels up. That could be because, in their haste to land from a U-turn, the pilots simply forgot to lower them. Or it might be that, with insufficient thrust from either engine, there wasn’t enough hydraulic pressure to lower them. (Wheels – but not flaps – on a 737 can be lowered without hydraulics by pulling a rip cord on the cockpit floor which opens the hatches and lets them drop out by gravity. But apparently, this can’t be reached from sitting in the pilots’ seats so maybe no time to get up and do it when you’re performing a U-turn.)

But there was apparently enough hydraulic pressure available to control the plane’s ailerons and elevators to direct it onto the runway at the right attitude so the other (more likely?) possibility about why no wheels or flaps is that they were deliberately kept up because, with no (or not enough) power from either engine, the pilots wanted to keep the plane as aerodynamically ‘clean’ as possible so that it would glide as far as possible to reach the runway and not land short of it.

And finally, the plane landed very far down the runway. No doubt very difficult to plant it on the correct spot when you’re going very fast due to no flaps. If it had landed in correct place, it MIGHT have been going a bit slower when hit that concrete bund with the antennae and there MIGHT have been fewer fatalities. (I gather a plane will take much longer to slow down skidding along its bottom than rolling on its wheels with its brakes applied – do pilots get trained that?)

So two overall possibilities: the pilots apparently disregarded all their training and made a complete and utter howling fuck of the whole thing from the moment of the (first?) bird strike – went around when they should have continued to land; did a U-turn when they should have gone all the way round (or had to do a U-turn because they shut down the wrong engine); and in their haste, forgot to put the flaps and wheels down again …

Or, more charitably, they erred by not continuing to land and going around instead but then, after that mistake was irretrievable, found themselves with no (or very little) power due to multiple bird strikes so HAD to do a U-turn and keep the flaps and wheels up to ‘stretch the glide’. But unfortunately, just stretched it a little too far, which might be forgivable under pressure.

The latter is the more plausible scenario, I think. (I’m thinking about the British Airways 777 which lost power on approach to Heathrow in 2008. The co-pilot there managed to ‘stretch the glide’ almost to perfection by pulling up the flaps (but not the wheels because that would have momentarily created more drag as the wheel well hatches opened) and dropped it onto the grass at the near end of the runway which wrote off the aeroplane but with no loss of life or even serious injury.)

BA38 almost made it to the runway

What about Sully, Miracle on the Hudson? He lost both engines due to multiple bird strikes. He judged he was too far away from the runway he’d just taken off from to do a U-turn back to it so he landed on the river where there were no obstacles to hit. Maybe the Korean pilots should have aimed for the sea instead (easy to be wise with benefit of hindsight). Maybe the takeaway from this accident is that, if you find yourself with no power, don’t aim for a runway where there’s too much of a risk of getting it slightly wrong and hitting something around the runway. Instead aim for open water (or, I gather, landing on trees if you can’t make a runway is very effective because they break up the momentum by the branches ripping off the wings and engines and whatnot but leaving the fuselage intact. Don’t try it at home, though.)

We haven’t mentioned the concrete bund thing at the end of the runway the plane crashed into. That’s what killed everybody. I get the argument that runs: (1) runways are designed so that you can stop in their length and if you can’t do that, then don’t try to land on them; and (2) if you’re going to keep space clear around a runway, you might as well tarmac over it to build a longer runway (in relation to which point (1) will then re-apply). But on balance, I think I’d be in favour of not gratuitously putting obstacles around a runway unless absolutely necessary. I gather these antennae don’t need to be mounted on anything and are themselves designed to be ‘frangible’ (breakable if hit by anything heavy like a 737).

Tom Hanks as Sully in the movie