Narrative:

Our flight left lax for our destination, akl (aukland, nz). After entering oakland oceanic airspace, we were using a satellite datalink system for communication with, and control by, oakland control. This system is known as cpdlc (controller-pilot, datalink, communications), and is the first part of cns (communications, navigation, and surveillance). Cns are the components of fans-1 (future air navigation system). I endorse this system, and strive to follow the procedures which are designed to prevent errors. On this occasion, we followed the procedure, and still erred in our interpretation of the clearance. At XA38 UTC we were at (0630N 15740W) ie, 4.5 degrees (270 NM) north of christmas island. We had been given a block altitude FL310-FL350 and were climbing in small increments so as to remain near our optimum altitude, (for fuel conservation). We received the following message: XA38Z ATC uplink/cross 0100S at and maintain FL350/report reaching FL350. The message shown above is as close a duplication as possible of the actual printout. Our procedure is to print the message so as to confirm that the flight number is correct, read the printout, agree on the clearance, determine appropriate action, and respond to ATC. In this case, 'wilco.' what did we do wrong? Looking at the third line: '/cross 0100S at and maintain FL350,' we both 'saw' 10 degrees south not 01 (one) degree south. We agreed on 10 degrees south, built a fix at 10 degrees south, programmed the FMC (flight management computer) to be at FL350 at 10 degrees south, and on crew change, briefed the other crew accordingly. At XB53Z the relief crew was at FL343. They received the following message: XB53Z ATC uplink/verify you'll be crossing 01 south at FL350 for traffic. Notice how much easier to read this second message is. The relief crew climbed immediately, and reported level FL350 at XB55Z. Notes and conclusions: 1) the datalink requires 1-2 mins, plus typing or entry time to complete a message. Followed by decision making time, typing or entry time, and another 1-2 mins for the response. This is far better than the older techniques (still in use), but at 7-8 mi per min we'll cover 35-40 NM per exchange. 2) the original clearance was timely, and correct in content. However, the format of the message, combined with the font used by the printer, contributed to the error made by 2 pilots in reading the message. The format of the second message (probably free text), is less likely to be misunderstood. 3) with voice communications, the pilot's readback provides the 'system' an opportunity to 'catch' an error in the pilot's interpretation of a clearance. The datalink system does not provide this safeguard. The controller has to take it on faith that we 'interpret' the clearance correctly. Also, the pilot doesn't have the controller's 'roger' to confirm 2 things: a) the controller knows that the correct flight has the clearance. B) the controller has found no error in your interpretation of the clearance. Having just switched from domestic to international flying, the loss of items a and B above is noticeable. The printout should be less likely to be misunderstood than voice, but if it is, there is no way for the controller to catch it. 4) I will certainly be more careful when reading the printouts. At the same time, it would be prudent to uplink clrncs that are not ambiguous, nor prone to playing 'tricks' on one's eyes.

Google
 

Original NASA ASRS Text

Title: WDB FLC ON OCEANIC CTL USING DATALINK COM MISINTERPRETS THE PRINTED CLRNC AND HAS ALTDEV. FORMATTED PRESENTATION HARD TO READ.

Narrative: OUR FLT LEFT LAX FOR OUR DEST, AKL (AUKLAND, NZ). AFTER ENTERING OAKLAND OCEANIC AIRSPACE, WE WERE USING A SATELLITE DATALINK SYS FOR COM WITH, AND CTL BY, OAKLAND CTL. THIS SYS IS KNOWN AS CPDLC (CTLR-PLT, DATALINK, COMS), AND IS THE FIRST PART OF CNS (COMS, NAV, AND SURVEILLANCE). CNS ARE THE COMPONENTS OF FANS-1 (FUTURE AIR NAV SYS). I ENDORSE THIS SYS, AND STRIVE TO FOLLOW THE PROCS WHICH ARE DESIGNED TO PREVENT ERRORS. ON THIS OCCASION, WE FOLLOWED THE PROC, AND STILL ERRED IN OUR INTERP OF THE CLRNC. AT XA38 UTC WE WERE AT (0630N 15740W) IE, 4.5 DEGS (270 NM) N OF CHRISTMAS ISLAND. WE HAD BEEN GIVEN A BLOCK ALT FL310-FL350 AND WERE CLBING IN SMALL INCREMENTS SO AS TO REMAIN NEAR OUR OPTIMUM ALT, (FOR FUEL CONSERVATION). WE RECEIVED THE FOLLOWING MESSAGE: XA38Z ATC UPLINK/CROSS 0100S AT AND MAINTAIN FL350/RPT REACHING FL350. THE MESSAGE SHOWN ABOVE IS AS CLOSE A DUPLICATION AS POSSIBLE OF THE ACTUAL PRINTOUT. OUR PROC IS TO PRINT THE MESSAGE SO AS TO CONFIRM THAT THE FLT NUMBER IS CORRECT, READ THE PRINTOUT, AGREE ON THE CLRNC, DETERMINE APPROPRIATE ACTION, AND RESPOND TO ATC. IN THIS CASE, 'WILCO.' WHAT DID WE DO WRONG? LOOKING AT THE THIRD LINE: '/CROSS 0100S AT AND MAINTAIN FL350,' WE BOTH 'SAW' 10 DEGS S NOT 01 (ONE) DEG S. WE AGREED ON 10 DEGS S, BUILT A FIX AT 10 DEGS S, PROGRAMMED THE FMC (FLT MGMNT COMPUTER) TO BE AT FL350 AT 10 DEGS S, AND ON CREW CHANGE, BRIEFED THE OTHER CREW ACCORDINGLY. AT XB53Z THE RELIEF CREW WAS AT FL343. THEY RECEIVED THE FOLLOWING MESSAGE: XB53Z ATC UPLINK/VERIFY YOU'LL BE XING 01 S AT FL350 FOR TFC. NOTICE HOW MUCH EASIER TO READ THIS SECOND MESSAGE IS. THE RELIEF CREW CLBED IMMEDIATELY, AND RPTED LEVEL FL350 AT XB55Z. NOTES AND CONCLUSIONS: 1) THE DATALINK REQUIRES 1-2 MINS, PLUS TYPING OR ENTRY TIME TO COMPLETE A MESSAGE. FOLLOWED BY DECISION MAKING TIME, TYPING OR ENTRY TIME, AND ANOTHER 1-2 MINS FOR THE RESPONSE. THIS IS FAR BETTER THAN THE OLDER TECHNIQUES (STILL IN USE), BUT AT 7-8 MI PER MIN WE'LL COVER 35-40 NM PER EXCHANGE. 2) THE ORIGINAL CLRNC WAS TIMELY, AND CORRECT IN CONTENT. HOWEVER, THE FORMAT OF THE MESSAGE, COMBINED WITH THE FONT USED BY THE PRINTER, CONTRIBUTED TO THE ERROR MADE BY 2 PLTS IN READING THE MESSAGE. THE FORMAT OF THE SECOND MESSAGE (PROBABLY FREE TEXT), IS LESS LIKELY TO BE MISUNDERSTOOD. 3) WITH VOICE COMS, THE PLT'S READBACK PROVIDES THE 'SYS' AN OPPORTUNITY TO 'CATCH' AN ERROR IN THE PLT'S INTERP OF A CLRNC. THE DATALINK SYS DOES NOT PROVIDE THIS SAFEGUARD. THE CTLR HAS TO TAKE IT ON FAITH THAT WE 'INTERPRET' THE CLRNC CORRECTLY. ALSO, THE PLT DOESN'T HAVE THE CTLR'S 'ROGER' TO CONFIRM 2 THINGS: A) THE CTLR KNOWS THAT THE CORRECT FLT HAS THE CLRNC. B) THE CTLR HAS FOUND NO ERROR IN YOUR INTERP OF THE CLRNC. HAVING JUST SWITCHED FROM DOMESTIC TO INTL FLYING, THE LOSS OF ITEMS A AND B ABOVE IS NOTICEABLE. THE PRINTOUT SHOULD BE LESS LIKELY TO BE MISUNDERSTOOD THAN VOICE, BUT IF IT IS, THERE IS NO WAY FOR THE CTLR TO CATCH IT. 4) I WILL CERTAINLY BE MORE CAREFUL WHEN READING THE PRINTOUTS. AT THE SAME TIME, IT WOULD BE PRUDENT TO UPLINK CLRNCS THAT ARE NOT AMBIGUOUS, NOR PRONE TO PLAYING 'TRICKS' ON ONE'S EYES.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.