After learning that United Airlines was missing a plane, American Airlines headquarters extended the ground stop nationwide.
( ( After ( learning ( that ( ( United Airlines ) ( was ( missing ( a plane ) ) ) ) ) ) ) ( , ( ( American ( Airlines headquarters ) ) ( ( extended ( ( the ground ) ( stop nationwide ) ) ) . ) ) ) )
(ROOT (S (PP (IN After) (S (VP (VBG learning) (SBAR (IN that) (S (NP (NNP United) (NNPS Airlines)) (VP (VBD was) (VP (VBG missing) (NP (DT a) (NN plane))))))))) (, ,) (NP (NNP American) (NNPS Airlines) (NNS headquarters)) (VP (VBD extended) (S (NP (DT the) (NN ground)) (VP (VB stop) (ADVP (RB nationwide))))) (. .)))
United Airlines instituted a ground stop nationwide prior to learning of the missing plane.
( ( United Airlines ) ( ( instituted ( ( a ground ) ( ( stop ( nationwide prior ) ) ( to ( learning ( of ( the ( missing plane ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP United) (NNPS Airlines)) (VP (VBD instituted) (S (NP (DT a) (NN ground)) (VP (VB stop) (ADVP (JJ nationwide) (RB prior)) (PP (TO to) (S (VP (VBG learning) (PP (IN of) (NP (DT the) (VBG missing) (NN plane))))))))) (. .)))