<P> Since A ♭ major was not often chosen as the main key for orchestral works of the 18th century, passages or movements in the key often retained the timpani settings of the preceding movement . For example, Beethoven's Symphony No. 5 in C minor has the timpani set to C and G for the first movement . With hand - tuned timpani, there is no time to re-tune the timpani to A ♭ and E ♭ for the slow second movement in A ♭; accordingly, the timpani in this movement are reserved for the passages in C major . In Bruckner's Symphony No. 1 in C minor, however, the timpani are re-tuned between the first movement in C minor and the following in A ♭ major . </P> <P> Charles - Marie Widor considered A ♭ major to be the second best key for flute music . </P> <P> A ♭ major was the flattest major key to be used as the home key for the keyboard and piano sonatas of Domenico Scarlatti, Joseph Haydn and Ludwig van Beethoven, with each of them using the key for two sonatas: Scarlatti's K. 127 and K. 130, Haydn's Hob XVI 43 and 46, and Beethoven's Op. 26 and Op. 110, while Franz Schubert used it for one piano sonata . It was also the flattest major key to be used for the preludes and fugues in Johann Sebastian Bach's Well - Tempered Klavier, as flatter major keys were notated as their enharmonic equivalents . </P> <P> Felix Mendelssohn, Johann Nepomuk Hummel, John Field, and Friedrich Kalkbrenner each wrote one piano concerto in A ♭ (Mendelssohn's being for two pianos); they had the horns and trumpet tuned to E ♭ . Max Bruch's Concerto for Two Pianos in A ♭ minor has its last movement in A ♭ major, which is the parallel major; this concerto plays with the contrast between the two keys . </P>

B is the mediant in the sale of a-flat major