I think you might be misinformed.
Companies will state something to the effect of: "Do not use OPEN DES below final approach altitude (i.e. after passing FAP or FAF depending on type of approach) but use SPEED mode (i.e. LOC-GS, TRK-FPA, LOC-FPA, APPR NAV)". Basically below 2000' agl you don't want to be using open descent unless you are looking for trouble. Trouble because of you might find yourself in a high energy state with idle thrust at low altitude and long spool-up times, possibly resulting in CFIT, so yes a safety issue.
If the airport is at 8000' elevation, what you heard is correct. And if you use VS below 10000' agl you will be safe, but run the risk of overspeeding if you don't actively control your speed (OPEN DES), when needing to get down quickly (i.e. winding up the speed to kill height=energy). Make sense?
Hope that helps.
I don't see the need for a VS restriction at any altitude. In fact more people should be using VS at low altitudes when approaching cleared levels in congested airspace, rather than relying on ALT* to do the work. There is already so much excess energy available when climbing small step climbs at low altitude. It saves you from performing potential TCAS manoeuvres, filling in reports, wasting engine life, disrupting pax comfort & scaring others. But... it is prudent to use OPEN CLB or CLB when at altitude.
Last edited by square leg; 28th October 2007 at 13:14.