B737-800
Distraction
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem
Equipment / Tooling
ATC did not mention anything about this so I'm not sure if this is an issue; but usage of the iPad is involved so I wanted to report. Captain was flying; descending via Tyssn 3 arrival into LAS... Captain said it was his first leg into LAS after many years.... Descending in VNAV between CEJAY and KADDY; aircraft started to get high on the profile after transition altitude; which I called out. At some point the Captain switched to Level Change to catch up. I dialed in 12;000 in the Altitude Alert window; the next restriction. We both were using iPads per new procedures; though I did have paper charts out as backup. While this was going on; Captain's iPad auto locked; blanking his chart screen. I called out that we needed to level at 12;000. It started to overshoot and we may have gone up to two hundred feet below 12;000 (11;800) and returned to 12;000 in only seconds. The rest of the flight was uneventful. The LA Center Controller did not mention it and subsequently switched us to approach.While late night flying and the Captain's first trip into LAS may have been contributing factors; his iPad blanking at just the right time seemed to unsettle him a bit as he mentioned in later discussion. Better awareness among the pilots about ways to prevent the iPad from doing this may help the iPad transition to be more successful. If the iPad requires a passcode to show the charts again; it can be nearly impossible to quickly bring the screen back up; especially in turbulence. That segment of the star doesn't allow a lot of room for error due to a 'get down and slow down' requirement. I felt like I was aware of what was going on and thought 12;000 would be captured without overshoot; but we did go slightly below.
B737-800 flight crew momentarily descended 200 FT below altitude restriction on LAS Arrival while in Level Change mode. Loss of chart display on Captain's Ipad cited as a factor.