Trombone Ensemble Bass Trombone - Level 5 - Digital Download SKU: A0.1207819 Composed by Dorothy Heyward, Du Bose Heyward, George Gershwin, and Ira Gershwin. Arranged by Iain Jackson. Jazz. 15 pages. Iain Jackson #805941. Published by Iain Jackson (A0.1207819). A jazzy treatment of Gershwin's classic Summertime, from Porgy and Bess, for trombone quartet.3 tenor trombones plus a bass trombone. The 1st trombone part goes quite high - up to Bb, C (twice) and high Db (once), the other two tenor parts go up to a G above the stave (briefly). This is for a fairly advanced group.