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))))) (. .)))
The ground stop was extended nationwide upon learning of the missing plane.
( ( The ( ground stop ) ) ( ( was ( ( extended nationwide ) ( upon ( learning ( of ( the ( missing plane ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN ground) (NN stop)) (VP (VBD was) (VP (VBN extended) (ADVP (RB nationwide)) (PP (IN upon) (S (VP (VBG learning) (PP (IN of) (NP (DT the) (VBG missing) (NN plane)))))))) (. .)))