FMS question

[doriangray001]

I was reading an incident report on the ASRS Database and was a bit puzzled. A pilot on approach in to JFK entered BETTY instead of BETTE in the FMS and thus was off course. Here's my question since BETTY is somewhere in England, 6790NM away, wouldn't the FMS give him an "INSUFFICENT FUEL" warning and disengage LNAV?
I am not a pilot but I do a lot of flying on MS Flight Sim and am familiar with the FMS of a B747 and the B767(the aicraft in question), does a real life FMS function differently?

Narrative

WE WERE DEPARTING JFK. I WAS THE PF. WE ALSO HAD A THIRD PLT IN THE JUMPSEAT WHO WOULD LATER ACT AS INTL RELIEF PLT. ORIGINAL SID WAS MERIT 3, PUT TRANSITION ALLEX AS FILED. DURING TAXI, THE DEP RTE TO MERIT WAS CLOSED DUE TO WX. WE WERE SENT TO CLRNC DELIVERY TO GET A NEW ROUTING. THE NEW ROUTING WAS GIVEN AS 'RWY HDG FOR RADAR VECTORS, BETTE, NANTUCKET, ALLEX AS FILED. MAINTAIN 5000 FT ON THE BETTE 3.' I TYPED IN THE FIXES AS RECEIVED ON THE FMS. I DID NOT START BY SELECTING THE BETTE 3 BECAUSE I ENTERED THE FIXES AS THE CTLR READ THEM TO US. AFTER TKOF WE WERE GIVEN SEVERAL VECTORS AND THEN TOLD 'DIRECT BETTE.' THE PLT MONITORING SELECTED THE FIX IN THE FMS AND LNAV AS THE MODE. THIS GAVE US A TURN TO THE N, CONSISTENT WITH OUR ORIGINAL RTE. DURING THE TURN, THE PLT MONITORING NOTICED THAT HE COULD NOT DISPLAY BETTE ON HIS MAP. I THEN NOTICED THAT THE HDG DID NOT MAKE SENSE WITH WHERE I WAS FAMILIAR WITH THE LOCATION OF BETTE, 110 DEGS AT 39 NM FROM JFK. I STARTED AN IMMEDIATE TURN BACK TO THE SE. THE CTLR THEN CALLED US AND REAFFIRMED OUR CLRNC TO BETTE. I NOTICED AT THIS POINT THE DISTANCE TO BETTE WAS 6789 NM ON THE FMS. WE RE-ENTERED BETTE AND WENT DIRECT TO THE CORRECT WAYPOINT. I BELIEVE THAT I ENTERED BETTY INSTEAD OF BETTE. WHEN THIS IS DONE, 2 SEPARATE FIXES COME UP THAT ARE APPARENTLY ON THE OTHER SIDE OF THE GLOBE. ALTHOUGH WE USED NEW PROCS FOR CONFIRMING RWY, WAYPOINT AND SID BEFORE TKOF, WE DID NOT CONFIRM THE FIX AGAINST ANY LOGIC CHK. I SHOULD HAVE NOTICED THE INCORRECT SPELLING OF 'BETTY.' ALSO, WE DID NOT CONFIRM THE NAME OF THE SID IN THE FMS. HOWEVER, THIS DOES NOT ALWAYS WORK AT JFK, BECAUSE MINOR MODIFICATION OF THE SID (REMOVAL OF JFK AND INTERCEPTING THE INBOUND RADIAL TO A FIX) WILL DROP THE SID FROM THE FMS. HAD THE CTLR USED THE PHRASEOLOGY, 'CLRED THE BETTE 3 BETTE 3 DEP, ACK TRANSITION, DIRECT ALLEX,' I WOULD LIKELY HAVE SELECTED THE SID FIRST IN THE FMS AND PREVENTED MY MISTAKE. THE NEW YORK CTLR WANTED TO KNOW HOW WE ENDED UP OFF COURSE AS HE WAS INFORMED BY CTR THAT THIS IS A COMMON OCCURRENCE ON THIS DEP.

[Jason]

The FMS will provide course guidance to pretty much wherever you tell it to go.  I would think the pilot would notice the incorrect fix when the distance to the fix read a rather large number, which he did.

If the controller did clear the aircraft as noted in the ASRS report, I think it would have been best to query the controller to confirm the clearance was either for the BETTE3 departure or radar vectors to BETTE and then direct ACK, ALLEX.  As it was described, the second clearance sounded like a bunch of fixes and then "on the BETTE3 departure" which is confusing to say the least.  This is a good ASRS report, glad to see people reading them. 

[JetScan1]

Here's my question since BETTY is somewhere in England, 6790NM away, wouldn't the FMS give him an "INSUFFICENT FUEL" warning and disengage LNAV?

The FMC continually estimates the fuel at destination and the CDU message "INSUFFICIENT FUEL" will be displayed if the calculated fuel is less than the fuel reserve value entered on the PERF INET page. So in this case they should have gotten an "INSUFFICIENT FUEL" message on the ground as soon as they entered BETTY instead of BETTE, as the calculated distance would have been around 6700 miles further than flightplan. This does not effect the LNAV mode and it will stay engaged.

The FMC isn't that fast (on the versions I've used) so the message might not have come on until 15 to 20 seconds after the route had been changed, it's also displayed on the CDU scratchpad (not an EICAS message), which requires you to be looking at the CDU to notice it. During that high workload phase of flight just prior to takeoff and initial departure your attention is not normally directed at the CDU. However anytime a route is changed or a direct clearance is given it should be verified by both pilots prior to engaging LNAV.   

DJ
- B767 pilot

[doriangray001]

Thanks for the info guys!