Aircraft C ontrollability& Certification With All Engines Failure

[AeroTech]

Hi,

25.671 FAR (d): The airplane must be designed so that it is controllable if all engines fail. Compliance with this requirement may be shown by analysis where that method has been shown to be reliable.

I am wondering about the meaning of this regulation especially the bolded words on the context of this regulation. For example what’s the meaning of:

a)controllable: being able to control the aircraft and land at airport only or any place (field, water,..), or it means something different?

b)All engines fail: wondering if it includes birds strike, ash volcano, heavy rain/hail, maintenance mistakes, fuel mis-management/exhaustion,…etc or it means only failures that are related directly to engine such continuous surge, no/low pressure oil,…etc

c)May be shown: I guess a confusing word. If aircraft manufacturer can’t show this requirement by analysis, what’s the other alternative?

d)Analysis: What kind of analysis?

What’s the JAR that’s equivalent to FAR 25.671(d)?

What do you think about this regulation (FAR 25.671(d) or the equivalent JAR especially while looking at the past or recent incidents/accidents after all engines failures? FYI FAR 25.671(d) was issued on 04/01/1970.

Feedback appreciated
Regards

[singpilot]

Geez;

Lots of questions there.

Lets get to the common denominator first.

All engines fail. Means that. Who cares how, as long as end result is the same.

I guess the case could be made.. engine still attached to mounts or not (CofG and drag issues); maybe rotating or not (hydraulics and drag/fire issues). I think the intent is...

Is the loss of all engine power going to affect you being able to control the aircraft for the remainder of flight (until altitude, airspeed and ideas run out). Nothing in regs says where that happens (unless you wanted to discuss ETOPS and a REALLY bad day). Case could be made that APU and RAT requirements extend that time a little longer.

Seems straightforward all of a sudden. Some method to do just that must be available.



Then comes the pudding (as in proof's in the ....).

Demonstrate it. Not a big prob, actually. Production test flight usually accomplishes this.

Analysis is demonstration on paper. (acceptable to certification authority). Have no idea about JAR.

HTH.

[john_tullamarine]

First read AC 25-7 (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/74402) to find out what the FAA might think the rule means.

One needs to keep in mind that any FAR has to be read with the corresponding AC to get the initial story.

[singpilot]

CHAPTER 4 - DESIGN AND CONSTRUCTION
Section 1. GENERAL [RESERVED]
Section 2. CONTROL SURFACES [RESERVED]
Section 3. CONTROL SYSTEMS
34. GENERAL - § 25.671.
a. Explanation. This material deals with the all-engines out case of § 25.671(d). The intent of this rule is to
assure that in the event of failure of all engines, the airplane will be controllable and an approach and landing flare
possible. This may be done by analysis where the method is considered reliable.
b. Procedures. The airplane should be evaluated to determine that:
(1) It is controllable following the failure of all engines in the climb, cruise, descent, approach, and
holding configurations and can be flared to a landing attitude from a reasonable approach speed. The airplane must
be controllable when all engines fail in each of the specified configurations and in any specific configuration that is
to be selected and maintained following the failure of the engines in accordance with the AFM emergency operating
procedures.
(2) The effectiveness of the emergency power to drive the airplane control system, whether generated
from a windmilling engine or an auxiliary power supply, should be demonstrated in flight.
(3) For airplanes with fully powered or electronic flight control systems, the emergency procedures
section of the approved Airplane Flight Manual should contain the appropriate operating procedures and a statement
similar to the following:
"The airplane has a fully powered (or electronic) control system that is dependent upon engine windmill
RPM, or an auxiliary power supply, to provide the necessary source of control system power in the event
all engines fail in flight. A minimum airspeed of XXX knots IAS will provide adequate hydraulic or
electrical power for airplane controllability in this emergency condition."




Sounds reasonable. Is from the Advisory Circular referenced.

[AeroTech]

Hi,

Thanks for the feedback.

All engines fail. Means that. Who cares how, as long as end result is the same.

I was wondering about the definition of engine failure, does engine failure mean voluntary or involuntary engine shutdown, engines flame-out: that’s why I mentioned some causes (related to engines & aircraft, weather, crew or maintenance mistakes,…) that result in engine shutdown. Let say you had birds strike with high EGT, surge and/or vibrations: you may opt to keep engine(s) running to get some thrust with hydraulic/electrical… when you reduce the thrust (engine at idle). So you have engines failures but one or more engines are still running (even though not properly). Other may elect to shutdown engines because of the risk of engine separation and wing damage (torn or missing slat, flap,…) which may cause problem controllability.

Demonstrate it. Not a big prob, actually. Production test flight usually accomplishes this.

I thought they will shutdown one engine at time and restart it again. Do you shutdown all engines at the same time? If so at what altitude?

Explanation. This material deals with the all-engines out case of § 25.671(d). The intent of this rule is to assure that in the event of failure of all engines, the airplane will be controllable and an approach and landing flare possible. This may be done by analysis where the method is considered reliable.
b. Procedures. The airplane should be evaluated to determine that:
(1) It is controllable following the failure of all engines in the climb, cruise, descent, approach, and holding configurations and can be flared to a landing attitude from a reasonable approach speed. The airplane must be controllable when all engines fail in each of the specified configurations and in any specific configuration that is to be selected and maintained following the failure of the engines in accordance with the AFM emergency operating procedures
(2) The effectiveness of the emergency power to drive the airplane control system, whether generated from a windmilling engine or an auxiliary power supply, should be demonstrated in flight.
(3) For airplanes with fully powered or electronic flight control systems, the emergency procedures section of the approved Airplane Flight Manual should contain the appropriate operating procedures and a statement
similar to the following:
"The airplane has a fully powered (or electronic) control system that is dependent upon engine windmill RPM, or an auxiliary power supply, to provide the necessary source of control system power in the event
all engines fail in flight. A minimum airspeed of XXX knots IAS will provide adequate hydraulic or electrical power for airplane controllability in this emergency condition."

“in any specific configuration” do you think this phrash includes takeoff (or end of take-off and the beginning of climb? If so do you think it is possible to control aircraft in such configuration after all engines failure (let say after birds strike).

I am wondering if the information or guidelines in Advisory Circular are mandatory? Since it is called advisory circular and not regulation.

The reason of this thread is to know your opinions regarding this regulation (issued on 04/01/70) and considering all engines failure incidents/accidents… that occurred in the past.
One may ask what was added to 747-400 incident after flying through volcanic ash? I guess in this incident the crew were able to restart engine(s) (may be one engine?), otherwise they may faced big challenges.

Do you think that APU, RAT, windmilling engines played an important role on the successful ditching (A 320 in Hudson River)?

Volcanis ash or birds strike may affect the windmilling RPM (damaged blades…), also windmilling RPM is reduced on high bypass engines. I am assuming the advisory circular is talking about flight test with shutdown engine and not damaged (intact blades, no sized spool…).
I am also thinking about B 777 (BA) accident after the fuel flow get restricted by ice.

I apologize if this post is too long.
Feedback appreciated
Regards

[john_tullamarine]

I am wondering if the information or guidelines in Advisory Circular are mandatory?

Certainly not mandatory.

However, the FAA will accept the use of information in an AC. In respect of certification matters, the applicant doesn't have to use the AC but, if not, then expect to have a somewhat harder time convincing the FAA that your stuff is good. In general, unless there is some very good reason to do so, an applicant would usually follow the AC guidance.

It is important to realise that what you or I might think the rule means over an ale or a coffee is totally irrelevant other than for interest. What counts is what either the Regulator or a relevant Court determines.

[Old Aero Guy]

Suggest you see your own thread on Airliners.net.

Aircraft Controllability With All Engines Failure — Tech Ops Forum | Airliners.net (http://www.airliners.net/aviation-forums/tech_ops/read.main/262237/)