The LUXAIR F50 Accident

The Relevant AD

The CASA 212 has had a number (at least four attributed) crashes due to a similar problem (failure of that flt idle stop)

See these links ONE TWO THREE FOUR

or consolidated page here

So either:

a. the technicians left the CB (for the baulk) out during the previous day's servicing (and the pilots didn't notice it out) or

b. the CB had shorted out itself out (or tripped enroute) or

c. There was a short that kept the baulk in absentia through-out or

d. There was a shorting-out (that removed the GI baulk) when a flap handle (or something else was moved - at about 1000ft AGL on finals), or

e. For some unfathomable reason, during an ILS, the pilot intentionally selected ground idle.

Reference the AD below, which seems very pertinent to the LUXAIR F-50 accident (but there are two others at the link below also)

If you look closely at the "Warning": at the bottom there would seem to be a glaring anomaly (at least that's the way it appears to me). The pilots are being warned about selecting GROUND IDLE in flight because "In case of failure of the flight idle stop, this would lead to loss of control from which recovery may not be possible."

What they really meant to say was (perhaps): " Be careful selecting Flight Idle whilst in flight. If the Flight Idle Stop has failed you might inadvertently (drop below Flt Idle and) enter Ground Idle. This would lead to loss of control from which recovery may not be possible."

It's no subtle distinction IMHO. The hazard is in bringing the power-levers back to where the flight-idle stop SHOULD BE, not finding it there and unconsciously continuing to retard the P/L's looking for it - and consequently suddenly hearing the propeller note change and finding yourself dropping out of the sky. And in fact, that's just about what's guaranteed to happen any old time the FLT IDLE STOP disappears (CB pulled or tripped, shorted solenoid - or whatever). It might happen one engine at a time (=> severe asymmetry) / maybe BOTH.

I hope you see that point. Of course you'd have to run it past someone who knew the F50 system intimately. There may be a power-lever lift-ramp that I'm unaware of.

But prima facie, it appears to me to be another single-point CRITICAL FAILURE.

Airworthiness Directives

Header Information
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39 [63 FR 36551 NO. 129 07/07/98]
Docket No. 97-NM-139-AD; Amendment 39-10648; AD 98-14-15
RIN 2120-AA64
Airworthiness Directives; Fokker Model F27 Mark 100, 200, 300, 400, 500, 600, and 700 Series Airplanes, and Model F27 Mark 050 Series Airplanes

PDF Copy (If Available):

Preamble Information

Regulatory Information

98-14-15 FOKKER SERVICES B.V.: Amendment 39-10648. Docket 97-NM-139-AD.

Applicability: All Model F27 Mark 100, 200, 300, 400, 500, 600, and 700 series airplanes, and Model F27 Mark 050 series airplanes; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (b) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent loss of airplane controllability caused by the power levers being positioned below the flight idle stop while the airplane is in flight, accomplish the following:

(a) Within 30 days after the effective date of this AD, revise the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include the following statements as specified in paragraph (a)(1) or (a)(2) of this AD, as applicable. This action may be accomplished by inserting a copy of this AD into the AFM.

(1) For Model F27 Mark 100, 200, 300, 400, 500, 600, and 700 series airplanes, insert the following:

"Warning: Ground fine pitch must not be selected in flight. This may lead to loss of control from which recovery may not be possible."

(2) For Model F27 Mark 050 series airplanes, insert the following:

"Warning: Do not attempt to select ground idle in flight. In case of failure of the flight idle stop, this would lead to loss of control from which recovery may not be possible."

(b) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Standardization Branch, ANM-113.

NOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(c) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(d) This amendment becomes effective on August 11, 1998.

from this link

This AD (inadvertent autofeathering) may also be relevant (#2001-16-04)

This AD also (#2000-01-15) - "(2) Within 12 months after the effective date of this AD, install a new ground idle stop assembly and new placards on the top cover of the pedestal, in accordance with Fokker Service Bulletin SBF50-76-016, dated December 20, 1996."