Take another look at the sentence:
Whenever Mike _________ his Cessna 152, a small airplane, he worried about running out of fuel, hitting birds, and being abducted by alien spaceships.
The sentence requires the past tense of fly, an irregular verb. Flew is the simple past form.
|Verb||Simple Present||Simple Past||Past Participle|
Flied, the form you chose, is a spelling error. Before you continue, review the rules for irregular verbs.