ROUND PROXIMITY WARNING SYSTEM (EGPWS) IN THE G-1159 SERIES AIRCRAFT. CONCURRENTLY ACCOMPLISHED RADIO ALTIMETER UPGRADE BY REMOVING THE # 1 AND # 2 COLLINS RADIO ALTIMETER ALT-50 AND INSTALLING COLLINS RADIO ALTIMETER ALT-55B IAW COLLINS ALT-50/55 RADIO ALTIMETER SYSTEM INSTALLATION MANUAL 523-0775918- 004118 DATED 4/1