diff --git a/ArduCopter/AP_Arming.cpp b/ArduCopter/AP_Arming.cpp
index a21f201458..016f827f31 100644
--- a/ArduCopter/AP_Arming.cpp
+++ b/ArduCopter/AP_Arming.cpp
@@ -63,6 +63,7 @@ bool AP_Arming_Copter::run_pre_arm_checks(bool display_failure)
         & oa_checks(display_failure)
         & gcs_failsafe_check(display_failure)
         & winch_checks(display_failure)
+        & alt_checks(display_failure)
         & AP_Arming::pre_arm_checks(display_failure);
 }
 
@@ -605,6 +606,18 @@ bool AP_Arming_Copter::winch_checks(bool display_failure) const
     return true;
 }
 
+// performs altitude checks.  returns true if passed
+bool AP_Arming_Copter::alt_checks(bool display_failure)
+{
+    // always EKF altitude estimate
+    if (!copter.flightmode->has_manual_throttle() && !copter.ekf_alt_ok()) {
+        check_failed(display_failure, "Need Alt Estimate");
+        return false;
+    }
+
+    return true;
+}
+
 // arm_checks - perform final checks before arming
 //  always called just before arming.  Return true if ok to arm
 //  has side-effect that logging is started
@@ -729,8 +742,14 @@ bool AP_Arming_Copter::arm_checks(AP_Arming::Method method)
 bool AP_Arming_Copter::mandatory_checks(bool display_failure)
 {
     // call mandatory gps checks and update notify status because regular gps checks will not run
-    const bool result = mandatory_gps_checks(display_failure);
+    bool result = mandatory_gps_checks(display_failure);
     AP_Notify::flags.pre_arm_gps_check = result;
+
+    // call mandatory alt check
+    if (!alt_checks(display_failure)) {
+        result = false;
+    }
+
     return result;
 }
 
diff --git a/ArduCopter/AP_Arming.h b/ArduCopter/AP_Arming.h
index 9e7c9e914d..b55a9de865 100644
--- a/ArduCopter/AP_Arming.h
+++ b/ArduCopter/AP_Arming.h
@@ -51,6 +51,7 @@ protected:
     bool mandatory_gps_checks(bool display_failure);
     bool gcs_failsafe_check(bool display_failure);
     bool winch_checks(bool display_failure) const;
+    bool alt_checks(bool display_failure);
 
     void set_pre_arm_check(bool b);
 
diff --git a/ArduCopter/Copter.h b/ArduCopter/Copter.h
index a4d1773fef..7e70dfd5de 100644
--- a/ArduCopter/Copter.h
+++ b/ArduCopter/Copter.h
@@ -863,6 +863,7 @@ private:
     bool position_ok() const;
     bool ekf_position_ok() const;
     bool optflow_position_ok() const;
+    bool ekf_alt_ok() const;
     void update_auto_armed();
     bool should_log(uint32_t mask);
     MAV_TYPE get_frame_mav_type();
diff --git a/ArduCopter/mode.cpp b/ArduCopter/mode.cpp
index 619f1baab1..5a71cf7787 100644
--- a/ArduCopter/mode.cpp
+++ b/ArduCopter/mode.cpp
@@ -250,6 +250,17 @@ bool Copter::set_mode(Mode::Number mode, ModeReason reason)
         return false;
     }
 
+    // check for valid altitude if old mode did not require it but new one does
+    // we only want to stop changing modes if it could make things worse
+    if (!ignore_checks &&
+        !copter.ekf_alt_ok() &&
+        flightmode->has_manual_throttle() &&
+        !new_flightmode->has_manual_throttle()) {
+        gcs().send_text(MAV_SEVERITY_WARNING, "Mode change failed: %s need alt estimate", new_flightmode->name());
+        AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
+        return false;
+    }
+
     if (!new_flightmode->init(ignore_checks)) {
         gcs().send_text(MAV_SEVERITY_WARNING,"Flight mode change failed %s", new_flightmode->name());
         AP::logger().Write_Error(LogErrorSubsystem::FLIGHT_MODE, LogErrorCode(mode));
diff --git a/ArduCopter/system.cpp b/ArduCopter/system.cpp
index 6a1ed570b8..174eeb2355 100644
--- a/ArduCopter/system.cpp
+++ b/ArduCopter/system.cpp
@@ -385,6 +385,21 @@ bool Copter::optflow_position_ok() const
     }
 }
 
+// returns true if the ekf has a good altitude estimate (required for modes which do AltHold)
+bool Copter::ekf_alt_ok() const
+{
+    if (!ahrs.have_inertial_nav()) {
+        // do not allow alt control with only dcm
+        return false;
+    }
+
+    // with EKF use filter status and ekf check
+    nav_filter_status filt_status = inertial_nav.get_filter_status();
+
+    // require both vertical velocity and position
+    return (filt_status.flags.vert_vel && filt_status.flags.vert_pos);
+}
+
 // update_auto_armed - update status of auto_armed flag
 void Copter::update_auto_armed()
 {