Quite a number of years ago, on leaving the HUET (then in the submarine escape tower) at HMS Vernon, a group of us watched a newly introduced-to-service (this ages me) Sea King being marshalled down from the hover to a landing on a concrete helipad. We immediately noticed that the u/c wasn't down. We yelled and waved to no avail, the marshaller had his back to us. A loud clattering noise obviously woke up the crew and the marshaller (who must have thought that Sea Kings didn't have wheels). Having briefly made metal to concrete contact, it shot up to a hover again, the wheels came down and it landed. Oops.