Narrative:

There is a significant risk of incorrect stab trim setting for takeoff on the embraer 190 that I believe requires clarification. My first officer and I noticed it after de-icing a 190 this evening. The takeoff trim setting must be within a green band to prevent a takeoff configuration warning. On the 190; the band ranges from 4 degrees to -2 degrees; with the range on the 190 spanning both positive and negative values. This leaves two significant ambiguities that don't seem to be addressed in any of our manuals or training. First; the trim setting comes through ACARS; and ACARS does not place a sign or label next to the value. On a 190 this evening ACARS sent us a stabilizer trim setting of 1.9. Having spoken to 2 dispatchers afterwards; they have never noticed a sign; positive or negative; or any label next to any trim setting sent by ACARS. We assumed the setting of 1.9 was positive; but one major concern is that both a 1.9 'up' and a 1.9 'down' trim will pass the takeoff configuration test; and I am unclear on how ACARS would indicate a negative trim value.the second problem is the one we encountered; and it's tied to the fact that our procedures have us set the trim to full down on cold nights and for deicing. When bringing the trim up to its takeoff position from full down after deicing; which takes several cycles of the trim switch due to its 3-second cutout; [and] it first passes through the negative portion of the green band. Since our trim setting was 1.9 (again; no value indicated on ACARS); we first stopped at the negative value of 1.9; which; again is also in the green band. Noticing the error; we then brought the trim to 1.9 'up'. An important side issue regarding how or if ACARS indicates a negative trim is that the EICAS doesn't. It actually displays 'dn' or up' with no + or - sign. The point is it is extremely easy to set the trim after deicing in the 'dn' portion instead of the 'up' portion since that's the first setting passed through when resetting the trim. In a worst-case scenario; 2.0 dn could be selected instead of 2.0 up and still pass the takeoff configuration test. This 4-degree error would require significantly more force on the yoke for rotation; which the pilot could incorrectly interpret as a problem with cg; weight; or flap setting; possibly causing a high speed abort on a contaminated runway.in the short term; please let us know how ACARS indicates a negative trim value for takeoff if it's at all possible; and post a memo highlighting the risk of setting the wrong trim value. Make ACARS transmit 'up' or 'dn' along with every stabilizer trim setting so there is no ambiguity. Even if the 190 won't ever indicate a 'dn' setting for takeoff trim; this should still be done for clarity. Also; emphasize the potential risk of incorrect trim setting after deicing or cold overnight on the 190 with a bulletin in the fom.

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Original NASA ASRS Text

Title: EMB190 Captain describes a 'gotcha' that can occur when setting the trim for takeoff after deicing. The green band trim settings for this aircraft are minus 2 to plus 4 or DN 2 to UP 4; but the 'plus' or 'minus' distinctions are not transmitted in the ACARS weight and balance.

Narrative: There is a significant risk of incorrect stab trim setting for takeoff on the Embraer 190 that I believe requires clarification. My First Officer and I noticed it after de-icing a 190 this evening. The takeoff trim setting must be within a green band to prevent a takeoff configuration warning. On the 190; the band ranges from 4 degrees to -2 degrees; with the range on the 190 spanning both positive and negative values. This leaves two significant ambiguities that don't seem to be addressed in any of our manuals or training. First; the trim setting comes through ACARS; and ACARS does not place a sign or label next to the value. On a 190 this evening ACARS sent us a STAB trim setting of 1.9. Having spoken to 2 Dispatchers afterwards; they have never noticed a sign; positive or negative; or any label next to any trim setting sent by ACARS. We assumed the setting of 1.9 was positive; but one major concern is that both a 1.9 'up' and a 1.9 'down' trim will pass the takeoff configuration test; and I am unclear on how ACARS would indicate a negative trim value.The second problem is the one we encountered; and it's tied to the fact that our procedures have us set the trim to full down on cold nights and for deicing. When bringing the trim up to its takeoff position from full down after deicing; which takes several cycles of the trim switch due to its 3-second cutout; [and] it first passes through the negative portion of the green band. Since our trim setting was 1.9 (again; no value indicated on ACARS); we first stopped at the negative value of 1.9; which; again is also in the green band. Noticing the error; we then brought the trim to 1.9 'UP'. An important side issue regarding how or if ACARS indicates a negative trim is that the EICAS doesn't. It actually displays 'DN' or UP' with no + or - sign. The point is it is extremely easy to set the trim after deicing in the 'DN' portion instead of the 'UP' portion since that's the first setting passed through when resetting the trim. In a worst-case scenario; 2.0 DN could be selected instead of 2.0 UP and still pass the takeoff configuration test. This 4-degree error would require significantly more force on the yoke for rotation; which the pilot could incorrectly interpret as a problem with CG; weight; or flap setting; possibly causing a high speed abort on a contaminated runway.In the short term; please let us know how ACARS indicates a negative trim value for takeoff if it's at all possible; and post a memo highlighting the risk of setting the wrong trim value. Make ACARS transmit 'UP' or 'DN' along with every STAB trim setting so there is no ambiguity. Even if the 190 won't ever indicate a 'DN' setting for takeoff trim; this should still be done for clarity. Also; emphasize the potential risk of incorrect trim setting after deicing or cold overnight on the 190 with a bulletin in the FOM.

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.