Large Transport
Flight Crew Last 90 Days 234; Flight Crew Type 2400
Confusion; Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert
Airport; Procedure
Departing LAX; Runway 24L; which is the primary runway for departures is closed due to construction.  We were given instructions to taxi to Runway 24R.  Our instructions were to taxi via the concrete pad to 24R.  That's it.  We were never given instruction to hold short of anything or even monitor another frequency for further instruction.  We taxied across 24L; which is closed for construction and I switched us to Tower frequency. Tower then asked us if we were on frequency and then advised us we needed permission to cross Runway 24L.  With the airport in an irregular operation; having a runway closed; the instruction we received from Ground Control was not as clear as it could have been. The construction was the biggest threat we faced.  As well as what we later thought was incomplete instruction from ATC.  After discussing the situation later; we both felt that the Ground Controller should have given more precise instructions; given the construction and irregular operations on the field.  If the Ground Controller had specified to either hold short or stay with him for further instruction or even switch to Tower for crossing; the whole situation would have been avoided.  Instead we incorrectly taxied with what we thought we had clearance to do. That was taxi to 24R via the concrete pad. That is what we did.
After pushing back from Gate X into the alley way; we started both engines and called for taxi.  We were told to taxi to Runway 24R via the concrete pad.  Runway 24L was NOTAMed; closed due to construction.  We taxied all the way to 24R and as we were holding short; we were told by Tower that we didn't have permission to cross 24L.  There were no aircraft taxiing ahead of us; so we had no example or advanced clue that we were not cleared to taxi all the way to the runway for which we were cleared.
Pilots report of taxiing to a runway but crossing a closed runway in the process at LAX.