Air carrier on descent for bwi expressed concern regarding ATC handling with regard to weather avoid...

Narrative:

This is a match with 844880We were operating on the EMI 5 arrival into bwi. There was a large thunderstorm just north of the arrival track in the vicinity of the mrb VOR. While I was making PA's to seat the passengers and flight attendants; the first officer requested and received clearance to deviate south of the arrival course to avoid the thunderstorm. We proceeded to parallel the arrival track about 5 miles south of the arrival; this seemed like it would provide safe separation from a distinct anvil cloud with mammatoform features and a precipitation shaft identified visually. At some point along our deviation; the approach controller instructed us to proceed direct ruane. I replied unable due to weather. Controller then instructed us to fly heading 040; I once again replied unable. Either of those 2 clearances would have placed us much too close to the thunderstorm. Controller then told us that they had traffic climbing to 170 and that they would be unable to provide separation. To say that the first officer and I were shocked is a grave understatement; I was honestly rendered speechless. We both immediately checked TCAS and outside visually; as it appeared we were on our own. No conflict was noted. The controller then told us other flights were operating closer to the cell; and that nothing was painting on radar. I did see one regional jet skirting the cell on a flight path I felt was unsafe. As to not painting that large cell; either the equipment was faulty or the controller was; to be blunt; lying. We were then handed off to another approach controller who was able to complete our handing uneventfully. I was very disturbed by this exchange. I will not ever permit ATC to place me on a course which I feel will jeopardize the safety of my airplane; and I feel this had the potential to do just that. I also was unaware ATC could simply wash their hands of aircraft separation.

Original NASA ASRS Text

Title: Air carrier on descent for BWI expressed concern regarding ATC handling with regard to weather avoidance; questioning ATC's comment reference aircraft separation.

Narrative: THIS IS A MATCH with 844880We were operating on the EMI 5 arrival into BWI. There was a large thunderstorm just north of the arrival track in the vicinity of the MRB VOR. While I was making PA's to seat the passengers and flight attendants; the First officer requested and received clearance to deviate south of the arrival course to avoid the thunderstorm. We proceeded to parallel the arrival track about 5 miles south of the arrival; this seemed like it would provide safe separation from a distinct anvil cloud with mammatoform features and a precipitation shaft identified visually. At some point along our deviation; the Approach Controller instructed us to proceed direct RUANE. I replied unable due to weather. Controller then instructed us to fly heading 040; I once again replied unable. Either of those 2 clearances would have placed us much too close to the thunderstorm. Controller then told us that they had traffic climbing to 170 and that they would be unable to provide separation. To say that the First Officer and I were shocked is a grave understatement; I was honestly rendered speechless. We both immediately checked TCAS and outside visually; as it appeared we were on our own. No conflict was noted. The Controller then told us other flights were operating closer to the cell; and that nothing was painting on radar. I did see one Regional Jet skirting the cell on a flight path I felt was unsafe. As to not painting that large cell; either the equipment was faulty or the Controller was; to be blunt; lying. We were then handed off to another Approach Controller who was able to complete our handing uneventfully. I was very disturbed by this exchange. I WILL NOT EVER permit ATC to place me on a course which I feel will jeopardize the safety of my airplane; and I feel this had the potential to do just that. I also was unaware ATC could simply wash their hands of aircraft separation.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	845169
Time
Date	200907
Local Time Of Day	1801-2400
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Medium Large Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	SID EMI
Flight Plan	IFR
Person 1
Function	Pilot Not Flying Captain
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 13000 Flight Crew Type 4000
Person 2
Function	Pilot Flying First Officer
Experience	Flight Crew Last 90 Days 65 Flight Crew Total 9800 Flight Crew Type 2750
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Inflight Event / Encounter Weather / Turbulence

Air carrier on descent for bwi expressed concern regarding ATC handling with regard to weather avoidance; questioning ATC's comment reference aircraft separation.