From 909f1ad1e5f5830e79b52c011fd41b8cc65b201c Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Thu, 10 Sep 2015 14:22:13 +0100
Subject: [PATCH] Allow D2 in altitude values (>62k ft)

---
 mode_ac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mode_ac.c b/mode_ac.c
index c2e3a8f..7c376e0 100644
--- a/mode_ac.c
+++ b/mode_ac.c
@@ -39,7 +39,7 @@ int ModeAToModeC(unsigned int ModeA)
   unsigned int FiveHundreds = 0;
   unsigned int OneHundreds  = 0;
 
-  if (  (ModeA & 0xFFFF888B)         // D1 set is illegal. D2 set is > 62700ft which is unlikely
+  if (  (ModeA & 0xFFFF8889)         // check zero bits are zero, D1 set is illegal
     || ((ModeA & 0x000000F0) == 0) ) // C1,,C4 cannot be Zero
     {return -9999;}