### Instruction:

Extract the cause and effect entities from the following sentence:
Only aircraft capable of communicating and conducting 4-D trajectory operations via data communications may enter the High Performance Airspace (HPA), which may initially be established at higher en route altitudes

### Assistant:

KEYWORD: Only
VARIABLE: aircraft
CONDITION: may enter the High Performance Airspace (HPA)
AND: and
NOT_RELEVANT: which may initially be established at higher en route altitudes
CAUSE_1: aircraft capable of communicating
CAUSE_2: conducting 4-D trajectory operations via data communications
EFFECT_1: may enter the High Performance Airspace (HPA)


### END
