diff --git a/ArduCopter/ReleaseNotes.txt b/ArduCopter/ReleaseNotes.txt
index 9c38f431e3201834451e7456824f6fb8a73dc876..a9a2ddb245e40cbe69dbc2ced6f77dc78a7fc808 100644
--- a/ArduCopter/ReleaseNotes.txt
+++ b/ArduCopter/ReleaseNotes.txt
@@ -1,4 +1,13 @@
 ArduCopter Release Notes:
+------------------------------------------------------------------
+ArduCopter 2.9.1b 30-Feb-2013
+Improvements over 2.9.1:
+1) reduce INS_MPU6K_FILTER to 20hz
+2) reduce InertialNav Z-axis time constant to 5 (was 7)
+3) bug fix for alt_hold being passed as int16_t to get_throttle_althold_with_slew
+4) bug fix for throttle after acro flip (was being kept at min throttle if pilot switched out of ACRO mode while inverted)
+5) reduce yaw_rate P default to 0.20 (was 0.25)
+
 ------------------------------------------------------------------
 ArduCopter 2.9.1 & 2.9.1-rc2 01-Feb-2013
 Improvements over 2.9.1-rc1: