Some trivia for the day.... Obviously when mentioning periscopes many people will think of submarines. They are however not the only vehicle using them. While it seems a bit strange the VC10 was designed to have a periscope included in its equipment. And not just one, but two! The reason behind this is fairly straightforward: as a pilot you sometimes want to see what's happening with your aircraft. And with that great big tail at the back, well, there's just no window through which you'll be able to get a look at what's happening up there. Normally this will not be a problem, but when you encounter icing conditions you might want to know how this is affecting your aircraft. The wings can be seen through the cabin windows, but not the tail and for this there is the periscope. Normally the periscope will be stored in its box somewhere in the back of the aircraft. In A4O-AB, the Sultan of Oman's aircraft, this box is kept in the aft galley. The periscope itself is about two and a half feet in length, and is a pretty sturdy piece of ironmongery. There are two mountings for the periscope in the roof of the fuselage, which are similar in design, both to be found just in front of the rearmost toilets in the aircraft. These can be revealed by undoing two quick-release catches on one of two small triangular panels in the roof. This provides the sight below. The periscope mounting in the roof of the aft fuselage, this is the left hand one, there is a similar one just three feet to the left of this one (looking towards the tail) The large hole on the right is the actual mounting into which the periscope is inserted. Once inserted partly, a catch is released and then the large lever can be pulled down which opens the small hatch and allows the periscope to be fully inserted, which has it protruding some three to five inches from the fuselage top. A catch keeps the periscope from falling down again, this catch is released with the small lever on the left, after which the hatch can be closed again. Preferably this is done before the periscope is completely removed from the mounting as it can get a bit drafty otherwise. In the photo above, the small notice reads: 'Periscope operation - The large handle operates the pressure flap - The small handle operates the catches'. In its installed position the periscope can be rotated 360 degrees, and the control on the side tilts the mirror at the top about 60 degrees up and down. All together you can look all the way around the aircraft, except for straight up at the sky (but there shouldn't be much to look at up there anyway). By switching from one mounting to the other both sides of the fin can be viewed. From the lefthand mounting, looking to the right wingtip will have you looking at the base of the fin as the periscope sticks up right next to it. This same periscope can also be mounted in two other locations. The first of these is in the cockpit roof. The mounting installed here was meant originally for use with a periscopic sextant, but will also take the periscope. During BOAC crew training flights where Dutch Roll characteristics were demonstrated trainees were sometimes given a chance to view the back end of the plane from here to see the effects. The second location is located in the bottom of the fuselage and was included to enable the crew to check the status of the landing gear if any uncertainty about its position was present amongst the crew. It consisted of an opening in the electronics bay access hatch located underneath the fuselage. Unlike the others there was no pressure shutter to cover this opening - it was just a plug which could be removed and replaced with the periscope - since it would generally only be used at lower altitudes where the pressure differential would be lower. Still it has been confirmed to me by an ex-BOAC First Officer that the plug could be removed when flying at 39000 feet, although this needed quite a pull and the result was quite noisy! And what about the second periscope then? To find this piece of equipment we will have to look around the back galley area. Somewhere in this area there will be a small piece of floor covering (about 6 by 6 inches) that can be lifted up. Underneath is then a small tube with a prism at the bottom that can be lowered into the aft cargo hold. The reasoning behind this small periscope is the fire-surpressing capability of the cargo hold. If a fire should exist in the cargo hold then the detection system will pick this up, but there are no extinguishing agents at hand to use. Basically the cargo hold is designed to be sealed so that the fire will die from oxygen starvation. As a fire warning can also be due to a faulty detection system the periscope is a simple device that can confirm or deny the existence of fire. Another reason for looking through it could be to confirm that a fire has actually died out, as a quick landing might be in order if it hasn't. Mind, I myself wouldn't want to be there on the floor watching a fire eating away at the aircraft I'm on.