To fly or not to fly....

[teh_flyguy]

Simple question, where does the line get drawn. Scenerio is that an aircraft has a system failure that is discovered on climbout from a remote site, the problem also occurred 2 days prior and was repaired by company maintenance and the aircraft flew an 8 hour day with no fault before the day of the recurrant failure. MEL states the system needs not be operational with the requirement that an operational test is performed, and the instructions in the MEL state what to do and what to look for. Airplane returns to point of departure, passengers are deboarded and operational test is performed on the ground successfully. Flight crew refuses to fly the plane home even though the ground test worked flawlessly with the MEL instructions. What would you have done?

For those familiar with type, Beech 200 with a bleed air fail. No pneumatic pressure indicated with side effected switched off, and with bleeds off aircraft would not pressurize, bleed on systems worked normally.

Only looking for an opinion. If the aircraft works as the MEL says it should, is it not deemed safe for flight? The defect has a history (abeit short) but the MEL test proves the system is isolated, what reason is there for refusing the trip?

[square]

I'd go if the weather was VFR, but if you're gonna be dodging TS maybe not such a good idea.

[teh_flyguy]

Good point. I would like to add, VFR all over the province. ~300nm flight, roads visible the whole way.

[Flying Nutcracker]

I thought that's what the MEL was for, to actually fly an aircraft that has a defect. So if the F/Os clock was MELd would they refuse to fly as well???

[Flybabe]

You can fly unpressurised. Unfortunately, this is one problem that might have to be troubleshot in the air... at the very least, get as much information as you can ( as you are doing).

If you're VFR, and you depart with all systems operational, fine. This is a case that the AME's need all the information you can give them. Pay attention.

[xsbank]

Seems to me that if the mel has been complied with, the aircraft could be flown as long as there are no other operational considerations that might make the flight unsafe. Did the crew say why they refused? Was it the 8 hours of flying they had already done? Did they like the new female camp cook and decide to stay over?

If there was no good reason to not do the flight, re-education is in order, methinks.

"For those familiar with type, Beech 200 with a bleed air fail. No pneumatic pressure indicated with side effected switched off, and with bleeds off aircraft would not pressurize, bleed on systems worked normally."

I do not know the BE20 but that sounds like a loss of redundancy? Can you explain to us curious/ignorant types a little more? My understanding, bleeds off=no pressurization seems logical; bleeds on system worked normally? Eh? How else would the a/c pressurize? Interesting.

[Rockie]

Think of the MEL as a document that tells you when you can't fly. It is always up to you to determine when you can fly based on the circumstances at the time. A short list of immediate circumstances that are not provided for in the MEL but could affect your decision are:

Weather
Defect history
Other defects that will increase the complexity and your workload
Airfield conditions
Your experience level
Aircraft general condition not provided for in the MEL
Nature of the flying you are about to embark on
Most importantly, your confidence in the aircraft

Remember, the MEL was written many years ago by a committee of people locked up in a room who probably don't even have a pilot's licence. Whether or not to fly today is, and will always be, your decision.

[GA MX Trainer Dude]

Another mis-understood Document - The MEL

The purpose of the MEL is to enable safe flight for an aircraft that has technical difficulties. Without the MEL system the aircraft would have to have all of the systems working as listed in the aircraft Type Certificate. Thus a faulty de-icer boot system that would not inflate a boot would have to be repaired before the next flight when not operating under a MEL system. Even if that flight is in the middle of the summer and no ice is present anywhere! The system is certified by TC after submission by the operator - the process involves a number of people and you can bet your last buck on the fact that there is a substantial pilot input into it.

At the end of all the discussion - you cannot use the MEL to force a crew to take an airplane just because it is "Legal" with the MEL process. The flight crew has the final say in the matter - PERIOD!!!!!

Reasons for not flying the aircraft are usually a safety concern - a flight path concern (mountains, water etc.) - and a workload concern. What we would do under the circumstances is of no importance - what matters is why the crew would be reluctant to fly the aircraft under the conditions??

The Beech 200 series aircraft has a less than stellar record regarding pressurization issues as presented by this Australian Report - see page 7 of the report - page 18 of the document

http://www.atsb.gov.au/publications/200 ... 060142.pdf

In addition this is the report of the 200 that left Perth Australia - didn't pressurize or stay pressurized and flew until it ran out of fuel. All on board were dead long before the crash.

http://www.atsb.gov.au/publications/inv ... 03771.aspx

Exerpt Here:

On 4 September 2000, a Beech Super King Air 200 aircraft, VH-SKC, departed Perth, Western Australia at 1009 UTC on a charter flight to Leonora with one pilot and seven passengers on board. Until 1032 the operation of the aircraft and the communications with the pilot appeared normal. However, shortly after the aircraft had climbed through its assigned altitude, the pilot’s speech became significantly impaired and he appeared unable to respond to ATS instructions. Open microphone transmissions over the next 8-minutes revealed the progressive deterioration of the pilot towards unconsciousness and the absence of any sounds of passenger activity in the aircraft. No human response of any kind was detected for the remainder of the flight. Five hours after taking off from Perth, the aircraft impacted the ground near Burketown, Queensland, and was destroyed. There were no survivors.

The investigation found that the pilot was correctly licensed, had received the required training, and that there was no evidence to suggest that he was other than medically fit for the flight. The weather presented no hazard to the operation of the aircraft on its planned route. The aircraft’s flightpath was consistent with the aircraft being controlled by the autopilot with no human intervention after the aircraft passed position DEBRA. After the aircraft climbed above the assigned altitude of FL250, the speech and breathing patterns of the pilot displayed changes that were consistent with hypoxia, but a rapid or explosive aircraft cabin depressurisation was unlikely to have occurred.

Testing revealed that Carbon Monoxide and Hydrogen Cyanide were highly unlikely to have been factors in the occurrence, and the absence of irritation in the airways of the occupants indicated that a fire in the cabin was also unlikely. The possibility of the pilot alone being incapacitated by a medical condition such as a stroke or heart attack would appear unlikely, given that there was no apparent activity or action by the other occupants of the aircraft for the duration of the flight.

The investigation concluded that while there are several possible reasons for the pilot and passengers being incapacitated, the incapacitation was probably a result of hypobaric hypoxia due to the aircraft being fully or partially unpressurised and their not receiving supplemental oxygen. Due to the extensive nature of the damage to the aircraft caused by the impact with the ground, and because no recording systems were installed in the aircraft (nor were they required to be), the investigation could not determine the reason for the aircraft being unpressurised, or why the pilot and passengers did not receive supplemental oxygen.



So it is possible that the crew is being very careful regarding this flight - That they had the balls to say no speaks to me of a professional outlook - or they really liked the camp cook???


MX

[xsbank]

Good post, GA. I did not mean to impugn the crew that refused to fly but I was genuinely interested in the mechanics of the bleed/pressurization system. (There is a guy at work who flew them so I can ask him tomorrow). It sounded to me like it would still work off one side, I was questioning why that was not enough?

Annyhoo, off to bed.

[GA MX Trainer Dude]

xs bank


Yes the other working side - if working correctly - and if the cabin leak rate is within limits - and sometimes both have problems - then 1 side will indeed supply sufficient airflow for pressurization. Of course you are down to 1 feed system - which means that if it goes away you are stuck at altitude without a means of pressurization.

Flow paks in the 200 are notorious for their failure rate - so that would also be a concern to the crew. FYI - there is a cabin leak rate check that is done - it is in the maintenance manual - you fly the aircraft to the specified altitude - and turn off both bleed air flow paks - then allow the Cabin Rate of Change to stabilize. If the Cabin Rate of Change is too high then the pressure vessel has too many leaks!!! Time to find out why. In addition there is a flow measuring venturi located under the floor on the right hand side of the aircraft that you can connect a manometer to. This will allow you to troubleshoot and determine the flow rates of the flow paks while in operation. Often the aircraft will go for extended times without any problems and then everything seems to give trouble at the same time.

If I had to fly the aircraft - I would not be off the oxygen from 8000' and up - And I would not subject passengers to the risk of hypoxia. I do know what I am talking about as I have done the High Altitude training course - was many years ago but nothing has changed in the way the human body re-acts to a lack of oxygen since then!!

I used to work for a photo survey company and sit above 20,000' in a Navajo - unpressurized - on O2 for several hours at a time. You get very well aquainted with how your body reacts when you do this for a while. Gave me a whole lot more respect for WWII crew who had to do their job at altitude in unpressurized aircraft.

xs - I didn't think you were slagging the flight crew - it looked like an honest request for information - on the MEL process - so that is how I wrote my reply. Hope this will give you enough info on the tecnical side. If not PM me and I can give you further info. I have taught the B200 MX Initial course so have lots of info on the airplane.

MX

[square]

Is this the King Air that had the bleed air fail in buffalo narrows? I heard they shut down the engine, declared an emergency, turned around back for YVT and shut er down on the runway. Sounds like a bit of an overreaction, but perhaps a bleed air failure is a warning of more serious problems?

[xsbank]

Thanks for that, GA, that explains it.

As for shutting off an engine for a bleed leak, I don't know the BE20 well enough to comment but bleed air can be upwards of 350 degrees and that can ruin your day, depending upon where it vents. The QRH will have directed their actions, likely.

[GA MX Trainer Dude]

BLEED AIR FAIL - lights are for an overheat system annunciation - they don't tell you that you have selected bleed air off or that the bleed air is not flowing!!!


This is a most screwed up system.

There are plastic lines - EVA tubing - that are placed strategically along the hot bleed air lines running in the airframe. If a bleed air line was to leak - the hot bleed air would melt the tubing. The tubing is connected to the regulated pneumatic pressure and each side has a pressure switch installed. The end of the tube is plugged.

The operation is simple;

1. - no engines running or both bleed air and enviro air switches in the off position - Fully down - you will have the 2 BLEED AIR FAIL annunciators illuminated. Reason - no pneumatic pressure flowing into the EVA tubing.

2. - any engine running and the applicable bleed air and enviro air switch selected to "Enviro OFF or Bleed Air ON" will allow the bleed air to flow into the pneumatic system - it only takes 1 bleed air switch to be positioned out of the very lower position to get this. Under this condition with the bleed air EVA tubes and plug, and switch working - the pneumatic system will pressurize the tubing - activate the low pressure switches and "BOTH" BLEED AIR FAIL annunciators will go out.

3. - any one engine running - or more - and a leak happens in the bleed air delivery system - the EVA tubing will melt - the air pressure will drop - and the affected side "BLEED AIR FAIL" light will illuminate - this indicates to the flight crew that they have an "OVERHEAT" condition and is a failure of the EVA tubing integrity.

The above makes the assumption that the regulated bleed air system is working correctly.

THERE IS NO INDICATOR ON THIS AIRCRAFT TO TELL YOU THAT THE BLEED AIR ENVIROMENTAL SUPPLY IS NOT ON OR IS ON!!!!!!

It is very possible to have both bleed air switches in the "ENVIRO OFF" position - giving no pressurization flow into the aircraft - and have the "BLEED AIR FAIL" lights out because the pneumatic system is still getting air as the switch position is in the center.

If both bleed air switches were in the full down position then you would have both "BLEED AIR FAIL" lights on as no pneumatic air would be delivered.

Yes it is a very stupid system - and has caught more than one pilot!!! The only thing that tells you that you actually have a bleed air flow - is by doing the Cabin Pressurization Test - after engine starts and before takeoff - if the cabin doesn't pressurize then you may have a problem with the inflow bleed. It's a pretty important test IMHO.

Lack of cabin pressurization is only going to indicated by the "CABIN PRESS" red warning - and the flashing master warning system light as the aircraft cabin climbs above about 12,000 feet. There is no aural warning and in bright sunlight the lights can be missed fairly easily.

Hope that this helps in understanding why the flight crew might just be a bit gun shy around the system!!

Common problems of the system are of course the EVA tubing, - pressure switch failures, - indication light failures, - and finger trouble.

Mx

[GA MX Trainer Dude]

I forgot to add that the bleed air lines in this aircraft run close to the forward spar of the wing. They pick off about 600 degrees of P3 air from the PT6 - its gets cooled off a bit but is still very hot.

FYI - 2024 T3 aluminium - what the spar is made of - is heat treated aluminium - and above about 350 degrees it will start to anneal and lose strength!!!!


Not a very good thing to have happen in your aircraft!!! In addition the hot air is pretty hard on electrical wiring etc. as well!!!

Mx