Ice formation over the Fuel Tank MD-80
Thread's got off track. This may bring it back.
Why only JAS? Why only MD-80 series? Why in January? Why on an otherwise remarkably reliable engine?
OK. No speculation - some background facts:
The MD-80 has long been known to have severe cold soaking of the upper wing root surface in the area of the centre tank -which extends into the roots. Also in the inboard area above the wing tanks, where the fuel gathers due to dihedral. This happens especially after long flights, where the remaining fuel gets undercoooled.
At temperatures up to 10 deg C (it has even happened to me at 14 deg C in drizzle in Tunis) in any appreciable moisture - even mist, very clear ice forms on the affected surface and cannot be detected without a hands on check. If not removed, the ice remains snugly in place and cracks off as the wings bear the weight on lift off - only to be blown straight into the waiting intakes a few metres further back. It can happen to your Fokker 100 too.
This was the cause of the famous SAS accident in Stockholm and has caused many other documented occurences of engine damage.
For this reason, MDC offered or approved various packages including:
- a fuel recirc system, which forces warmer fuel from ground tanking to flow by the wing root area.
- an ice detector on a piezo basis to warn of tank top area icing.
- various tassels and flags on the wing upper surface to make ice easier to identify.
NON of these methods guarrantees there to be no ice in the critical area. The only way is the hands on check - via a ladder - a vehicle or (which no-one likes because of the possibility of wrong re-fitting) through the emergency exit window.
Some companies rigidly enforce this hands on check up to six degrees - some to 10 degrees and some to 15 degrees. Some do not.
So far no speculation - just facts.
Now let's take a look at Japan - a very long country running from sub tropical Okinawa (as far as MD-80 ops are concerned) up to Hokkaido in the north, where the houses are all double glazed.
The shortest leg on the network is about 20 minutes - the longest over 2 hours - time enough for the phenomenon mentioned above to occur.
MDC and Pratt once issued a bulletin about the "soft ice phenomenon", where even non-brittle ice and slush entering the compressor causes nicks, scratches and eventually cracks.
Still not speculating - it seems to me that:
a) Grounding the fleet is a tremendous over-reaction on such a well tried and well known airframe / engine combination
b) The American colleagues are correct to handle this as an separate - maybe airline related case.
Yes I have flown there. Yes on MD-80 and seen how seriously or otherwise the ice problem has been taken. Yes it may have some completely different cause.
By the way using max reverse when idle would suffice and never using reduced thrust on Takeoff doesn't shorten engine life either.
Just background.
FC.