What are PVDs?
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What are PVDs?
Just reading a BALPA newsletter which says (talking about Low Visibility Take Offs) Some aircraft types are equipped with additional guidance systems such as PVDs, so check that they stream in the correct direction during the line up monoeuvre.
But what are PVDs?
But what are PVDs?
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It is a "para visual display". It looks like a barbers pole on it's side and is driven by the localiser. It unshutters as you turn onto the runway and offers "left a bit", "right a bit" guidance as you hurtle down the runway in low vis conditions.
It closes when airborne.
Usually mounted on the edge of the coaming.
Rod
It closes when airborne.
Usually mounted on the edge of the coaming.
Rod
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...developed by Collins and first fitted to Grumman Gulfstream 1 aeroplanes in 1963. Works like a charm. BA/GF TriStars (amoung others) also had PVD.
Originally developed by Smiths (I think).
Originally developed by Smiths (I think).
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I think the PVD instructer said...The first point of reference on low vis takeoff is the center line lighting.
The runway centerline can be confirmed by tuning the takeoff runway ILS and displaying the two PVD barbers poles,(black and light yellow),which would stream in the correct sense to guide you onto the centerline, if you were off it or lined up on the runway edge lights or on a taxiway, ie Frankfurt RW18.which did for one DC8 crew.
If on the centerline the Pvd would display but not stream when activated by the pilot.
You could also do a very short roll forward with a little bit of a left/ right to test the streaming.
Useing the centerline lights for initial reference the pilot benifited by the streaming effect of the centerline lights comeing up fast as the aircraft accelerated. However if the vis reduced during the roll the pilots eye reference was shortened, as he progressively reduced his range to find and see the centerline lights, as this occured his perifferal vision picked up on the pvds and he received excellent guidence in the correct sense,in poorer vis conditions his eyesight range could reduce further into the cockpit and would fall naturally onto his magnetic heading indicator and he could still see and sense from the Pvds and remain guided onto the centerline.The greater the error the more rapid the stream.
If vis improved the pilots eye scan was simply reversed in the oposite sequence to aquire the centerline lights.
The Pvd is used in the same way in an aborted takeoff at high speed in low vis conditions,where the decreasing speed reduces the streaming effect in reverse of the centerline lights. Again the Pvd helps keep you straight and on the centerline.
The low vis takeoffs in our company were always at full thrust, never reduced, and the power was set for the hp.
The Pvd was also armed for use on low vis landings and again they helped guide the pilot to the centerline on the landing roll out if the autopilots fell out for any reason after touchdown on the auto land.
There was also a ground run monitor that was used in low vis taxi, takeoff and landings. It is 25years since BA did my L1011 training and 13years since I flew a L1011,hopefully the above is helpful to you, but is only recalled from memory, so could be wrong.
The runway centerline can be confirmed by tuning the takeoff runway ILS and displaying the two PVD barbers poles,(black and light yellow),which would stream in the correct sense to guide you onto the centerline, if you were off it or lined up on the runway edge lights or on a taxiway, ie Frankfurt RW18.which did for one DC8 crew.
If on the centerline the Pvd would display but not stream when activated by the pilot.
You could also do a very short roll forward with a little bit of a left/ right to test the streaming.
Useing the centerline lights for initial reference the pilot benifited by the streaming effect of the centerline lights comeing up fast as the aircraft accelerated. However if the vis reduced during the roll the pilots eye reference was shortened, as he progressively reduced his range to find and see the centerline lights, as this occured his perifferal vision picked up on the pvds and he received excellent guidence in the correct sense,in poorer vis conditions his eyesight range could reduce further into the cockpit and would fall naturally onto his magnetic heading indicator and he could still see and sense from the Pvds and remain guided onto the centerline.The greater the error the more rapid the stream.
If vis improved the pilots eye scan was simply reversed in the oposite sequence to aquire the centerline lights.
The Pvd is used in the same way in an aborted takeoff at high speed in low vis conditions,where the decreasing speed reduces the streaming effect in reverse of the centerline lights. Again the Pvd helps keep you straight and on the centerline.
The low vis takeoffs in our company were always at full thrust, never reduced, and the power was set for the hp.
The Pvd was also armed for use on low vis landings and again they helped guide the pilot to the centerline on the landing roll out if the autopilots fell out for any reason after touchdown on the auto land.
There was also a ground run monitor that was used in low vis taxi, takeoff and landings. It is 25years since BA did my L1011 training and 13years since I flew a L1011,hopefully the above is helpful to you, but is only recalled from memory, so could be wrong.
