AN ACR FLC SUSPECTS THAT THE DRIFTDOWN CALCULATIONS FOR THE RTE TO BJX MAY BE FAULTY BECAUSE THE DECISION LINE IS DRAWN BEFORE HIGH TERRAIN IS ENCOUNTERED.

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LOCATION: OVER NLD; MEXICO. FLTS TO BJX FROM DFW HAVE AN ENRTE DRIFTDOWN DECISION POINT THAT IS JUST 8 MI S OF NLD. THIS SEEMS PRETTY USELESS TO ME AS THE TERRAIN THAT WOULD BE A FACTOR IN THE EVENT OF AN ENG FAILURE STARTS AT MTY AND WOULD CONTINUE TO BE A FACTOR UNTIL NEAR SLP. IF TERRAIN IS NOT A FACTOR; THEN WHY HAVE THE DECISION POINT? IF IT IS A FACTOR; THE DECISION POINT SHOULD BE BTWN MTY AND SLP WHERE IT WOULD BE OF USE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT HIS COMPANY HAD RECENTLY BEEN USING A COMPUTER GENERATED DRIFTDOWN CALCULATION THAT IS OCCASIONALLY ERRONEOUS. IN THIS CASE; THE DECISION LINE IS DRAWN BEFORE THE ACFT WOULD GET OVER ANY HIGH TERRAIN. THE CAPT INQUIRED OF HIS COMPANY IF THIS MEANT THAT THE HIGH TERRAIN S OF THE PRESENT GO/NO-GO LINE WAS NOT A PROB FOR THE F100 ACFT AT NORMAL CRUISE ALTS OF FL310 AND FL330. HE HAS NOT RECEIVED AN ANSWER YET. THE MINIMUM OFF-RTE ALT ALONG THIS PORTION OF THE RTE IS AS HIGH AS 14200 FT NEAR SLP AND 12800 FT AT HIS DEST; BJX. THE RPTR SAID THAT HIS NORMAL SINGLE ENG CRUISE ALT ON A STANDARD DAY IS AROUND 21000 FT.