Citizens of most countries do not need a transit visa through Germany. Only citizens of few countries do. For citizens of India, you do need one unless you meet certain conditions (holding AP is such a condition).
Only passport holders of the following countries
DO need a German transit visa
unless they hold a visa for another EU country,
or they hold a US green card or reentry permit,
or they have unrestricted residency permits in Andorra, Japan, Monaco, Canada, San Marino, or Switzerland :
Afghanistan
Angola
Bangladesh
Columbia
Congo, Democratic Republic
Cuba
Eritrea
Ethiopia
Gambia
Ghana
India
Iran
Iraq
Jordan
Lebanon
Nigeria
Pakistan
Somalia
Sri Lanka
Sudan
Syria
Turkey
For citizens of India and Turkey, you don't need a transit visa if you hold an Advanced Parole document and are flying to the US. You also don't need a transit visa if you are merely returning from a legal stay in the US to your home country through Germany.
For other passport holders of countries listed above, there may also be some other
exceptions.