How do you form the past perfect tense of verbs?
According to Raymond Murphy grammar book--intermediate level,
if you like to use past perfect tense form, you need two facts that occurred in the past one after one but not simultaneously or intercepts one to other.
Like, when I was writing the answer, my wife was sleeping.
Or you don't know the specific time, you can use both past simple forms too.
I asked him something when he came at my door yesterday. I know yesterday but don't know specific time.
But I had reached to the airport premise before the plane landed on the the ground.
This is the perfect example of past perfect verb form.
Hope it works.