diff --git a/pyModeS/decoder/commb.py b/pyModeS/decoder/commb.py
index 4957681..d49d293 100644
--- a/pyModeS/decoder/commb.py
+++ b/pyModeS/decoder/commb.py
@@ -36,3 +36,5 @@ from pyModeS.decoder.bds.bds60 import *
 # MRAR and MHR
 from pyModeS.decoder.bds.bds44 import *
 from pyModeS.decoder.bds.bds45 import *
+
+from pyModeS.py_common import fs, dr, um
diff --git a/pyModeS/decoder/surv.py b/pyModeS/decoder/surv.py
index ceec90c..4e54614 100644
--- a/pyModeS/decoder/surv.py
+++ b/pyModeS/decoder/surv.py
@@ -3,6 +3,7 @@ Decode short roll call surveillance replies, with downlink format 4 or 5
 """
 
 from pyModeS import common
+from pyModeS.py_common import fs, dr, um
 
 
 def _checkdf(func):
@@ -19,91 +20,6 @@ def _checkdf(func):
     return wrapper
 
 
-@_checkdf
-def fs(msg):
-    """Decode flight status.
-
-    Args:
-        msg (str): 14 hexdigits string
-    Returns:
-        int, str: flight status, description
-
-    """
-    msgbin = common.hex2bin(msg)
-    fs = common.bin2int(msgbin[5:8])
-    text = None
-
-    if fs == 0:
-        text = "no alert, no SPI, aircraft is airborne"
-    elif fs == 1:
-        text = "no alert, no SPI, aircraft is on-ground"
-    elif fs == 2:
-        text = "alert, no SPI, aircraft is airborne"
-    elif fs == 3:
-        text = "alert, no SPI, aircraft is on-ground"
-    elif fs == 4:
-        text = "alert, SPI, aircraft is airborne or on-ground"
-    elif fs == 5:
-        text = "no alert, SPI, aircraft is airborne or on-ground"
-
-    return fs, text
-
-
-@_checkdf
-def dr(msg):
-    """Decode downlink request.
-
-    Args:
-        msg (str): 14 hexdigits string
-    Returns:
-        int, str: downlink request, description
-
-    """
-    msgbin = common.hex2bin(msg)
-    dr = common.bin2int(msgbin[8:13])
-
-    text = None
-
-    if dr == 0:
-        text = "no downlink request"
-    elif dr == 1:
-        text = "request to send Comm-B message"
-    elif dr == 4:
-        text = "Comm-B broadcast 1 available"
-    elif dr == 5:
-        text = "Comm-B broadcast 2 available"
-    elif dr >= 16:
-        text = "ELM downlink segments available: {}".format(dr - 15)
-
-    return dr, text
-
-
-@_checkdf
-def um(msg):
-    """Decode utility message.
-
-    Utility message contains interrogator identifier and reservation type.
-
-    Args:
-        msg (str): 14 hexdigits string
-    Returns:
-        int, str: interrogator identifier code that triggered the reply, and
-        reservation type made by the interrogator
-    """
-    msgbin = common.hex2bin(msg)
-    iis = common.bin2int(msgbin[13:17])
-    ids = common.bin2int(msgbin[17:19])
-    if ids == 0:
-        ids_text = None
-    if ids == 1:
-        ids_text = "Comm-B interrogator identifier code"
-    if ids == 2:
-        ids_text = "Comm-C interrogator identifier code"
-    if ids == 3:
-        ids_text = "Comm-D interrogator identifier code"
-    return iis, ids, ids_text
-
-
 @_checkdf
 def altitude(msg):
     """Decode altitude.
diff --git a/pyModeS/py_common.py b/pyModeS/py_common.py
index 0b299ee..b6af728 100644
--- a/pyModeS/py_common.py
+++ b/pyModeS/py_common.py
@@ -404,3 +404,85 @@ def wrongstatus(data: str, sb: int, msb: int, lsb: int) -> bool:
             return True
 
     return False
+
+
+def fs(msg):
+    """Decode flight status for DF 4, 5, 20, and 21.
+
+    Args:
+        msg (str): 14 hexdigits string
+    Returns:
+        int, str: flight status, description
+
+    """
+    msgbin = hex2bin(msg)
+    fs = bin2int(msgbin[5:8])
+    text = None
+
+    if fs == 0:
+        text = "no alert, no SPI, aircraft is airborne"
+    elif fs == 1:
+        text = "no alert, no SPI, aircraft is on-ground"
+    elif fs == 2:
+        text = "alert, no SPI, aircraft is airborne"
+    elif fs == 3:
+        text = "alert, no SPI, aircraft is on-ground"
+    elif fs == 4:
+        text = "alert, SPI, aircraft is airborne or on-ground"
+    elif fs == 5:
+        text = "no alert, SPI, aircraft is airborne or on-ground"
+
+    return fs, text
+
+
+def dr(msg):
+    """Decode downlink request for DF 4, 5, 20, and 21.
+
+    Args:
+        msg (str): 14 hexdigits string
+    Returns:
+        int, str: downlink request, description
+
+    """
+    msgbin = hex2bin(msg)
+    dr = bin2int(msgbin[8:13])
+
+    text = None
+
+    if dr == 0:
+        text = "no downlink request"
+    elif dr == 1:
+        text = "request to send Comm-B message"
+    elif dr == 4:
+        text = "Comm-B broadcast 1 available"
+    elif dr == 5:
+        text = "Comm-B broadcast 2 available"
+    elif dr >= 16:
+        text = "ELM downlink segments available: {}".format(dr - 15)
+
+    return dr, text
+
+
+def um(msg):
+    """Decode utility message for DF 4, 5, 20, and 21.
+
+    Utility message contains interrogator identifier and reservation type.
+
+    Args:
+        msg (str): 14 hexdigits string
+    Returns:
+        int, str: interrogator identifier code that triggered the reply, and
+        reservation type made by the interrogator
+    """
+    msgbin = hex2bin(msg)
+    iis = bin2int(msgbin[13:17])
+    ids = bin2int(msgbin[17:19])
+    if ids == 0:
+        ids_text = None
+    if ids == 1:
+        ids_text = "Comm-B interrogator identifier code"
+    if ids == 2:
+        ids_text = "Comm-C interrogator identifier code"
+    if ids == 3:
+        ids_text = "Comm-D interrogator identifier code"
+    return iis, ids, ids_text