There is always a risk when connecting on separate tickets, although less-so in the USA. US Airways may have something similar to the unpublished AA "flat tire" policy which allows late arrivals to standby for the next flight.
Even better would be to connect on AA, as the recently revealed
oneworld - Separate Tickets policy states:
If a customer is holding separate tickets on AA or another oneworld carrier, customers holding separate tickets where travel is on oneworld airlines should be treated as through ticketed passengers.