diff --git a/pyModeS/decoder/allcall.py b/pyModeS/decoder/allcall.py
index ebd132c..4e9fdf2 100644
--- a/pyModeS/decoder/allcall.py
+++ b/pyModeS/decoder/allcall.py
@@ -3,31 +3,61 @@ from pyModeS import common
 Decoding all call replies DF=11
 """
 
-
 def ipcode(msg):
-    '''Returns the IP code of the Mode S all-call reply (DF11)'''
-    binaryraw=common.hex2bin(msg)
-    PI=binaryraw[-24:]
-    DATA=binaryraw[:-24]
+    if common.df(msg) == 11:  # check that the msg is DF11
+        '''Returns the IP code of the Mode S all-call reply (DF11)'''
+        binaryraw=common.hex2bin(msg)
+        PI=binaryraw[-24:]
+        DATA=binaryraw[:-24]
 
-    Gx='1111111111111010000001001000'
-    Mx=DATA[::-1].zfill(len(DATA)+24)[::-1]
-    initialdifference=len(Mx)-len(Gx)
-    Gx = Gx[::-1].zfill(len(Mx))[::-1]
-    while len(Mx)>initialdifference:
-        MSB=Mx[0]
-        if MSB=='1':
-            result=int(Mx,2)^int(Gx,2)
-            Mx = str(bin(result)[2:])
-            Gx = Gx.rstrip('0')[::-1].zfill(len(Mx))[::-1]
+        Gx='1111111111111010000001001000'
+        Mx=DATA[::-1].zfill(len(DATA)+24)[::-1]
+        initialdifference=len(Mx)-len(Gx)
+        Gx = Gx[::-1].zfill(len(Mx))[::-1]
+        while len(Mx)>initialdifference:
+            MSB=Mx[0]
+            if MSB=='1':
+                result=int(Mx,2)^int(Gx,2)
+                Mx = str(bin(result)[2:])
+                Gx = Gx.rstrip('0')[::-1].zfill(len(Mx))[::-1]
 
-        else: #If the Mx starts with a 0
-            Mx=Mx[1:]
-            Gx=Gx[:-1]
+            else: #If the Mx starts with a 0
+                Mx=Mx[1:]
+                Gx=Gx[:-1]
 
-    SIcode=(int(Mx,2)^int(PI,2)) #Mx is the parity sequence and PI is the last field of the DF11.
-    return SIcode
+        SIcode=bin(int(Mx,2)^int(PI,2)).zfill(7) #Mx is the parity sequence and PI is the last field of the DF11.
+        if int(SIcode[0:3],2)>0:
+            return str("SI" + str(int(SIcode[3:],2)))
+        else:
+            return str("II" + str(int(SIcode,2)))
+    else:
+        raise RuntimeError("Incorrect or inconsistent message types")
 
+def flight_status(msg):
+    '''returns the flight status'''
+    if common.df(msg) == 11:  # check that the msg is DF11
+        binaryraw=common.hex2bin(msg)
+        CA = (int(binaryraw[5:8],2))
+        if CA in [0, 1, 2, 3, 6, 7]: #reserved
+            return None
+        if CA == 4:#level 2 transponder, ability to set CA to 7 and on ground
+            return "on ground"
+        if CA == 5:#level 2 transponder, ability to set CA to 7 and airborn
+            return "airborne"
+    else:
+        raise RuntimeError("Incorrect or inconsistent message types")
+
+def transponder_level(msg):
+    '''returns the transponder level'''
+    if common.df(msg) == 11:#check that the msg is DF11
+        binaryraw=common.hex2bin(msg)
+        CA = (int(binaryraw[5:8],2))
+        if CA in [1, 2, 3, 4, 5, 6, 7]: #reserved
+            return 2
+        if CA == 0:
+            return 1
+    else:
+        raise RuntimeError("Incorrect or inconsistent message types")
 
 def capability(msg):
     '''return the capability code'''
@@ -51,4 +81,7 @@ def capability(msg):
 
 def AA(msg):
     '''returns the icao code of the aircraft'''
-    return (msg[2:8])
+    if common.df(msg) == 11:  # check that the msg is DF11
+        return (msg[2:8])
+    else:
+        raise RuntimeError("Incorrect or inconsistent message types")