Let's simplify the situation greatly:
- IMC
- Engines out
Questions:
Is power available for flight instrumentation/computers?
Hydraulics & electric for controls?
Do they fly with the APU running, or can they fire it up quickly and in those conditions? Are there battery backups to keep the flight computer online?
Even if their pitot static systems are clear and they have attitude information, what can they do without adequate flight controls or power (thrust), especially in turbulence?
If the engines were to stop for whatever unlikely reason, the airplane does continue to fly. The only thing an airplane needs to fly is airspeed. Normally, the engines produce thrust which in turn gives airspeed, but without the engines altitude can be traded for airspeed. Just like on a roller coaster, as you go down, your speed increases. If you can go down at a controlled rate at an airspeed that produces the most lift with the least amount of drag (called L/D max, for maximum lift to drag ratio) most airplanes glide very well. A -16 has a glide ratio of akin to a 30,000 Lb metal cinder block (7 mile / 5,000'); well, perhaps a little better than a cinder block (it has wings). The pilot maintaines 210Kts + 4Kts / 1000 Lbs of gas and external stores (but only at 6o AoA). I've heard 737 have 15:1 glide ratio (15 miles glide per 1 mile altitude lost).
The details concerning engine out can be found in:
Following a dual engine failure the flight deck indications change drastically as generators drop off line, the RAT is deployed and ECAM prioritizes checklists. Control of the aircraft must be taken immediately by CM1, and a safe flight path established.Clearly if they are dealing w/unrealiable airspeed indicator scenario, they have some problems on their hands.It is important at this stage to correctly identify the failure as it can be easily confused with all engine generators fault. ECAM will prioritize checklists so to avoid confusion read ECAM carefully to correctly identify the failure. It is vital to establish good crew communications and to apply efficient task-sharing.