B747 Undifferentiated or Other Model
Training / Qualification; Situational Awareness; Confusion; Communication Breakdown
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Environment - Non Weather Related; Human Factors
Military Charter. On approach forgot to say Hector Pascals or HPA or QNH. Approach Controller issued 2997...and repeated back as 2997 when asked again. (997 HPA equals 2947 QNH and can be as much as 500 FT off of 299 7QNH). After verification; Controller said aircraft transponder reading low. Again confirmed altitude with Controller and 2;000 FT; cleared for Visual. Conditions were night VMC vertical visibility excellent; forward visibility 20 plus. Visual approach backed up with ILS; VASI's working. Noticed glideslope intercept off altitude for distance. Confirmed with Controller and then he said 997 without any units of measurement. Normal landing; segment completed with no other events.
Approximately 25-30 minutes out from our destination; I tuned and listened to the ATIS. With the difficulty of the language barrier; I listened to information HOTEL numerous times to understand the arrival runways. During my listening watch; the female voice said in these exact words: '..winds *******; altimeter niner niner seven (997). In addition; the flying First Officer and an additional First Officer listened to the ATIS numerous times to also confer and understand the communication gap. Shortly after hitting the arrival fix; we were vectored off and given radar vectors to Runway 33R. As we were given headings; we were also given descent clearances. Our last altitude given on base was 2;000 FT. On about a 5-6 mile base; Control asked us to verify our altitude as he was showing us level at 1;500 FT. I stated that we were level at 2;000 FT. Shortly thereafter he again asked our altitude as he still showed us at 1;500 FT. I stated we were level at 2;000 FT with an altimeter setting of two niner niner seven (29.97). I also said that I was switching to our alternate transponder. He gave us a final heading to intercept the ILS and said that we were still showing 1;500 FT and to contact the Tower. We continued and landed with no further inquiry and landed without incident. It was night; clear skies and the only other traffic was a previous arrival approximately 5 miles ahead of us. No other traffic was in the vicinity. After landing and parking at remote we understood the problem. Niner niner seven was in Hectopascals not inches. We had just left an international airport that reported altimeter settings in inches.
All four B747 pilots failed to recognize the foreign airport's 997 Hector Pascal altimeter and allowed 29.97 QNH to remain in the altimeter; despite ATC's repeated correction; which made the aircraft about 500 FT low on approach.