hello guys,
check out the following link (EASA Type Certificate Data Sheet):
http://www.easa.europa.eu/certificat...4-06042011.pdf
according to the EASA, the BAe.125 Series 800A and 800B (built in the UK) were originally certified to FL430, however the FAA only certified them for FL410 (check Note 69).
For those who can read German, the LBA documents (LBA TCDS) also show 43,000 for the 800B, but 41,000 only for the 800A:
www2.lba.de/data/bb/Flug_o2t/ta_2507_01.pdf (800A)
www2.lba.de/data/bb/Flug_o2t/ta_2507_02.pdf (800B)
(if the links don't work, just google the documents)
Checking the FAA's Type Certificates, all HS-125's are limited to FL410 period.
Being able to get to FL410 (with the exception of the 900XP, in most cases) depends on the combination of prevailing ISA conditions and actual takeoff weight. A very helpful guide is the "Maximum Takeoff Weight for Cruising Level" Table in the QRH. It might well be more beneficial to level-off at FL390 and do LRC there for a while and step-climb to FL410 after a good hour or so.