Why was the Boeing 737-700ER chosen instead of the 737-800 or 737-900?
Short answerPurchase price: the 737-700ER was cheaper to buy.
NotesThe question compares the Boeing 737-700ER with the 737-800 and 737-900 in the airborne early-warning discussion. The brief answer identifies purchase price as the reason for the choice. It does not compare their technical capabilities.