The Landing Signal Officer, or LSO is a commissioned officer, and is also a pilot. Each carrier based squadron will typically detail 2 or 3 junior officer pilots to be LSO as a collateral duty (which means they alternate this duty with flying). These officers will typically have demonstrated an above-average aptitude for carrier landings. A carrier's Air Wing staff will also have a senior LSO who supervises the LSO's of the various fighter, attack, antisubmarine, and other fixed-wing squadrons that make up the Air Wing. Helicopters, as you might expect, don't need or use LSOs.

There is a special training program for LSO's, where they learn the refined skill of spotting deviations from ideal technique. And, indeed, as a pilot you learn to trust the LSO, because he can detect whether you are going above or below the glide slope before you can by watching the meatball. He can tell by looking at the attitude of your airplane whether you are fast or slow, and he can spot every throttle movement you make by looking at the smoke from your exhaust.

LSO's are colloquially referred to as "paddles", because before the jet era they directed approaches by holding out colored signalling devices resembling a ping-pong paddle in each extended arm. Jets, though, fly so much faster that these devices became obsolete, and jet approaches are flown with reference to the optical landing system, aka the meatball, described in my w/u on carrier landings.

During landing operations a team of LSOs will be stationed on what is called the "platform", which is an area on the port edge of the flight-deck towards the stern. There is typically a wind-break to provide some shelter from the 30 knot winds that blow down the deck, as well as a control panel for the meatball apparatus, a radio for communications with planes on approach, and the "pickle", which is a switch they use to make the meatball flash to signal a wave-off. Another feature of the platform is a catch-net jutting out from the side of the ship a few feet under the platform. If it looks like they're about to get creamed, the LSO team can dive off the platform into this net.

LSO's are charged with grading each approach by every pilot no matter the seniority. Grades are simple, you can get an "OK", a "fair", a "no-grade", or, if you screw up totally, you'll get a "cut pass", which is probably your last attempt at a carrier landing. LSO's have an elaborate shorthand notation with which they record what you did during an approach. (There's probably a way to encode samples of this in HTML, but I'm not confident enough to try that at the moment.) A typical translation would be something like: "slightly high start, slow nose-high in the middle, nose-down come-down to land, no-grade." Which, when the pilot being debriefed is a Commander and the LSO is a Lieutenant, can lead to a tense moment, but, much like a baseball umpire, the LSO is ALWAYS right. An LSO will also detect longer term trends for each individual pilot - becuase much like a big-league ball player, you can have "slumps" and "hot streaks" in your approaches from day to day, week to week. So if you start to develop a bad habit, the LSO is there to snap you out of it. Or, failing that, ground you so you don't endanger anybody else.

As I say, there'll be a team of LSO's on the platform during landing ops, with representatives from each squadron. So when an S-3 rolls into the groove, the S-3 LSO will take the "pickle", signifying he is in charge. Another LSO will take shorthand dictation of the LSO's judgement of your pass when you land.

The LSO can give guidance over the radio to an approaching pilot, but won't unless necessary, since radio traffic is at all times kept to a minimum. You'll typically hear one of only three things over the radio from an LSO: "power", which means you're settling below the glideslope, give it some throttle, "right for line-up", which means you need to make a brief wing-dip to correct your line-up, and, finally, if you've balled it up, you'll hear "WAVE-OFF!". You can also generally tell the severity of the deviation by the pitch of the LSO's voice!

You MUST heed an LSO's command - failing to do so will get you washed out of Naval Aviation quicker than just about anything else you can do.

Finally, LSO's are not charged with any other duty involving taxi or parking of aircraft. There are dozens of other flight-deck personnel who handle that. The LSO is there entirely for safety during landing operations. It's an awesome responsibility, but there are many such jobs on a carrier.