Gerund & Infinitive Phrase In Subject - How Modified?

Hello,

"Navigating an airport to board a flight is certainly a vastly different experience today than it was before September 11, 2001."

I have a few questions regarding this sentence's grammar:

1. I think "Navigating an airport" is a gerund phrase acting as the sentence's subject. Correct?



2. I think "to board a flight" is an infinitive phrase, with "to board" being the infinitive, and "a flight" being the object of "to board" (to board what?).



3. Here's where I'm less sure about things: I want to say that the infinitive phrase acts here as an adverb telling "why" you are navigating an airport. However, I know adverbs modify adverbs, adjectives, and verbs, not nouns. So first, am I correct here, and if so, in this situation is the adverb modifying "navigating" by itself either as a verb or adjective? Would this not modify the whole phrase as "whole verb phrases" are often modified?

4. Are there two separate phrases here, the gerund phrase and infinitive phrase, or is this actually one single gerund phrase, with the infinitive being part of and modifying the gerund phrase?

Thank you for your time,

Jason