17749
In April 1996 , the programme was officially resumed in response to a fresh order from the Polish Air Force , which involved the purchase of six new-build aircraft and the retrofitting of 11 existing aircraft in air force service with improved engines , avionics and wings by 1998 .
 Polish Air Force
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Polish Air Force