A320 flight crew reports missing the crossing restriction at TRTLE during descent on the BASET 3 to LAX. The aircraft went into open descent while entering an ATC assigned runway change into the FMGC and was not detected by the flight crew.
Synopsis
A320 flight crew reports missing the crossing restriction at TRTLE during descent on the BASET 3 to LAX. The aircraft went into open descent while entering an ATC assigned runway change into the FMGC and was not detected by the flight crew.
Narrative
Crossed KONZL at 17;000 FT. ATC cleared us to descend via the BASET 3 Arrival and expect ILS 7R; we had briefed and programmed ILS 6L in FMS. I was pilot flying and dialed in 10;000 FT in the altitude window and pushed altitude; and then changed the runway to 7R in FMS. We were briefing the new runway when ATC said to maintain 14;000 FT as we missed our crossing restriction at TRTLE and he said he didn't want us to go below his airspace. We were at 14;500 FT at that time. No other aircraft were within 15 miles of us. We continued our descent to 14;000 FT and that was the end of the altitude deviation. I think the crossing restriction dropped out when I changed runways or went into open descent when the new runway was inserted and I didn't notice it. Then we were briefing the new approach we had just been assigned when we flew through the altitude. Task saturation and unfamiliarity with landing on the 6's and 7's in LAX as we almost always land on 24's and 25's contributed to this deviation.
Second reporter narrative
While descending into LAX airport we were switched to the Baset 3 arrival for 07R instead the Seaview 2 arrival as per our flight plan; a clearance to cross KONZL at FL170 was also issued which we complied with uneventfully. After passing KONZL at FL170 we were cleared to descend via the Baset 3 arrival but another runway change was issued for 06L at the same time. We switched the arrival in the MCDU and commenced our descent as per the arrival. After switching the runways we reviewed the altitude/speed restrictions and briefed the new approach; but the TRTLE restriction to cross at 16;000 got deleted and there are only 6 miles from KONZL to TRTLE and the descent already started; we were busy re-briefing and rechecking the restrictions and the Aircraft descended to 14;700 FT; the ATC Controller told us to level off at 14;000 to remain in his airspace; that we missed the restriction. The ND and MCDU did not show the restriction; it was deleted during the change. There was no loss of separation with other traffic and we proceeded to LAX without any further comment from ATC.The event occurred due to several factors: 1) Several arrival and runway assignment changes during the busy phase of descent. 2) Software feature on MCDU sometimes drops altitude and speed restrictions form certain fixes when runway or arrival is changed in the MCDU. Sometimes the arrival is selected and all the altitude/speed restrictions are missing and have to be manually entered. 3) We were distracted by the change of arrivals and runways and all the tasks that came along with that; like reprogramming and re-briefing the new procedure. 4) Time constraints were also an issue since we wanted to get the change done properly and promptly to review the restrictions since we were already on the descent phase; and TRTLE was very close to KONZL (only 6 miles away)1) Correct the MCDU software to avoid dropping altitude and speed restrictions when the present procedure is changed. Maybe develop a warning message to make pilots aware. 2) Make ATC aware on how these many runway and arrival changes impact our operational safety; especially when issued during high workload phases like descent. These changes are very common in LAX but they are usually given earlier with more time to prepare; at a phase were pilots are not that busy. 3) Pilots should delay all briefings and supplemental duties until all the restrictions are verified are correct and the aircraft is a position to meet them safely.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.