--- DarthVader/OrbitalInfo/src/igrf_sub.for	2014/08/29 07:06:41	1.10
+++ DarthVader/OrbitalInfo/src/igrf_sub.for	2014/10/31 14:02:53	1.11
@@ -196,6 +196,7 @@
       SAVE /FIDB0/
       COMMON/GENER/     UMR,ERA,AQUAD,BQUAD
       SAVE /GENER/
+      REAL FLS
 C
 C-- RMIN, RMAX ARE BOUNDARIES FOR IDENTIFICATION OF ICODE=2 AND 3
 C-- STEP IS STEP SIZE FOR FIELD LINE TRACING
@@ -203,7 +204,8 @@
 C 
       DATA RMIN,RMAX    /0.05,1.01/
       DATA STEP,STEQ    /0.20,0.03/
-        BEQU=1.E10
+      BEQU=1.E10
+      FLS = FL
 C*****ENTRY POINT  SHELLG  TO BE USED WITH GEODETIC CO-ORDINATES
       RLAT=GLAT*UMR
       CT=SIN(RLAT)                                              
@@ -304,6 +306,10 @@
       HLI=0.5*(((C3*T+C2)*T+C1)*T+C0)                            
       ZQ=Z*Z
       R=HLI+SQRT(HLI*HLI+ZQ)
+      IF(R.NE.R)THEN
+         FL = FLS
+         RETURN
+      ENDIF
       IF(R.LE.RMIN)GOTO30                               
       RQ=R*R
       FF=SQRT(1.+3.*ZQ/RQ)