Navy fliers fly a glideslope system called the fresnel lense or commonly called the meatball it is a glideslope indicator much like PAPI or VASI but it is very very precise as it is what guides you down to the landing area on the carrier, and hopefully the three wire. land with a centered ball on the lense you get the three wire, land just ever so sagging you get the two and if the ball is cresting you hopefully get the four wire but most often you get the hated bolter = you get another try at it If I am correct there is only 40 feet between wires. So when flying this type fo approach the throttles are constantly moving, for every correction ie: you suck power off to stop a rising ball or to descend ever so slightly you must correct that correction with at least a two part correction ie: you suck power to stop the rising ball now you must add more power than required to stop the rate of descent, catch the ball before it falls off the lense, then you must reset power to your neytral power setting before all that power you just added causes you to fly the ball off the top of the lense. I hope that makes sense. Anyways while adding power in short bursts in the S-3 it makes a very characteristic Whoop Whoop sound so we call the S-3 Viking the Hoover or Hoov for that reason. Heres a fresnal lense fi you want any more info about it just hollar. Wish I had a better pic but if you look almost all the way up on the left side you can see a row of horizontal lights with the meatball being the brightest, amber light slightly sagging from center. That is the Fresnel lense.

ZK