Narrative:

On the ground; we were cleared to climb via the snshn 1 RNAV departure by tower except climb and maintain 14;000 ft. On departure shortly after the pom hold down fix of 8;000 ft; socal directed us to change the transition from the filed and cleared las transition to the beale transition; and after livvi fix; cleared direct yelah then climb and maintain 14;000 ft. We were at a low altitude; I've never heard of changing transitions on the departure; we don't have time to load; execute; brief; and verify the new clearance prior to the branch point only seven miles away; so I said; 'unable.' ATC then step-climbed us to a higher altitude. ATC later said another flight was able to do the change; and I said we didn't have time. I say good for them.the next controller did the same thing; directed us to another fix on the departure; but since we now had time and were above 15;000 ft we complied. I asked that controller why the transition changed. They said they were using them to deconflict traffic. I asked; 'why didn't we receive the other transition on the ground?' he said they didn't know about the traffic then and that they were using transitions to deconflict on the fly. I asked; 'if I took the other transition; how high would we have been cleared?' he said 14;000 ft.this needs to stop as soon as possible; no pun intended. We go to great lengths to file; load; verify; brief; and execute the clearance. We take many minutes to setup on the ground in a stationary environment and cannot expect to; in the heat of the moment with two minutes to go to a branch point; change transition just to make it easier for ATC. This is a downright dangerous action by ATC.

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Original NASA ASRS Text

Title: B737-700 Captain reported he was uncomfortable with an ATC request to modify an ONT departure procedure during the climb; stating the increased workload at that time would be a safety issue.

Narrative: On the ground; we were cleared to climb via the SNSHN 1 RNAV Departure by Tower except climb and maintain 14;000 FT. On departure shortly after the POM hold down fix of 8;000 FT; SoCal directed us to change the transition from the filed and cleared LAS transition to the BEALE transition; and after LIVVI fix; cleared direct YELAH then climb and maintain 14;000 FT. We were at a low altitude; I've never heard of changing transitions on the departure; we don't have time to load; execute; brief; and verify the new clearance prior to the branch point only seven miles away; so I said; 'Unable.' ATC then step-climbed us to a higher altitude. ATC later said another flight was able to do the change; and I said we didn't have time. I say good for them.The next Controller did the same thing; directed us to another fix on the departure; but since we now had time and were above 15;000 FT we complied. I asked that Controller why the transition changed. They said they were using them to deconflict traffic. I asked; 'Why didn't we receive the other transition on the ground?' He said they didn't know about the traffic then and that they were using transitions to deconflict on the fly. I asked; 'If I took the other transition; how high would we have been cleared?' He said 14;000 FT.This needs to stop ASAP; no pun intended. We go to great lengths to file; load; verify; brief; and execute the clearance. We take many minutes to setup on the ground in a stationary environment and cannot expect to; in the heat of the moment with two minutes to go to a branch point; change transition just to make it easier for ATC. This is a downright dangerous action by ATC.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.