As a general rule, when a letter with a Fathah and next letter is Alif, then the sound of Fathah and Alif is stretched by two measures of harakah. 'aa'
Note: In this lesson, letter Alif is a true Alif (Madd).
If anytime the letter Alif appers with vowels or sukoon, this is not a true Alif but it is letter Hamza.
Letter Alif appears always empty and never the first letter in a word, It may come with Madd sign and always comes after another letter, whereas the letter Hamza may come as the first letter in a word.