Narrative:

I don't believe takeoff separation between departing aircraft from 18L and 18C was adequate. IFR departures were in effect. Aircraft Y was cleared previous to our departure. If clearance was adequate for the conditions in play; then aircraft Y has a drastically different climb profile than industry practice. Combine two different company profiles for performing departures along with an RNAV departure procedure from adjacent runways that are coincidental at the first RNAV point; and you have a recipe for unsafe separation. I assume that aircraft Y was the target which triggered a TA/RA alert at ribzz on the goetz 4 departure. This was a real head turner as the RA to increase vertical speed immediately followed the traffic alert. The first officer immediately made corrective action; but the target(s) turned red and appeared to merge. We were IMC from approximately 800 ft AGL until well after the RA. There is a lot happening with changing configurations; frequency handoff; and checklists. As a crew; we shouldn't have to be concerned with ATC separation under these kind of meteorological conditions in the condensed departure environment of the afternoon launch. ATC never made a call nor seemed concerned about the takeoff interval. I don't know how they could have missed it.I think exact attention to spacing intervals on departures should be prioritized in the departure environment that is the memphis hub. I think special attention should be given to regional jet departures interspersed in this condensed setting. Don't run VFR interval departures during IMC environment.

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Original NASA ASRS Text

Title: Pilot reported of being too close to preceding departure. Aircraft received a TA/RA on climb out. Reporter wondered if the ATC facility was running VFR separation during IFR conditions.

Narrative: I don't believe takeoff separation between departing aircraft from 18L and 18C was adequate. IFR departures were in effect. Aircraft Y was cleared previous to our departure. If clearance was adequate for the conditions in play; then Aircraft Y has a drastically different climb profile than industry practice. Combine two different company profiles for performing departures along with an RNAV departure procedure from adjacent runways that are coincidental at the first RNAV point; and you have a recipe for unsafe separation. I assume that Aircraft Y was the target which triggered a TA/RA alert at RIBZZ on the GOETZ 4 Departure. This was a real head turner as the RA to increase vertical speed immediately followed the traffic alert. The FO immediately made corrective action; but the target(s) turned red and appeared to merge. We were IMC from approximately 800 ft AGL until well after the RA. There is a lot happening with changing configurations; frequency handoff; and checklists. As a crew; we shouldn't have to be concerned with ATC separation under these kind of meteorological conditions in the condensed departure environment of the afternoon launch. ATC never made a call nor seemed concerned about the takeoff interval. I don't know how they could have missed it.I think exact attention to spacing intervals on departures should be prioritized in the departure environment that is the Memphis Hub. I think special attention should be given to regional jet departures interspersed in this condensed setting. Don't run VFR interval departures during IMC environment.

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.