Jul 21, 2007

Minimum Equipment List - MEL

The recent accident at Sao Paulo, Brazil, apparently involved an aircraft with a deactivated reverse thrust system.

Below is a typical MEL (Minimum Equipment List) page related to the Reverse Thrust system. These manuals are produced in a generic form by the aircraft manufacturers, then each aviation authority and airline within that aviation authority's jurisdiction might add restrictions specific to their concerns. This sample is from the British CAA's version for the Boeing 737-100 airplane (simply because that's the first one I found in an online format).

I don't recall if the Airbus A319 MEL has the same restriction against operations on slippery and flooded runways, but I strongly suspect it does (does anyone have a copy handy out there, to confirm or deny this?)...

I do know that the 319 has great short field landing capabilities with just the normal brakes, anti-skid system and ground spoilers. In fact when executing a max performance (short field) landing on the A319 on a DRY runway, the airplane decelerates so quickly that the reversers can't deploy fast enough to be of much use. That is, by the time the reverse 'kicks in' the airplane is below the minimum speed at which reverse thrust is effective.

I also know that hydro-planning will occur on a runway that has even a small amount of standing water. Once hydroplaning begins, the landing distance tables go out the window. In these conditions, reverse thrust is essential to slowing the airplane until the wheels can contact the pavement.

(click on the image for a full-size view)

11 comments:

John said...

If you check http://www.opspecs.com/AFSDATA/MMELs/Final/transport/A-320%20R19/ which is the FAA MMEL for the A320 you can only dispatch with an inop reverser if the other reverser is disabled. No mention of runway length.

Interestingly that MEL for a 737-100 seems to indicate that it is possible to use only one T/R. This may be due to the original design of the 737 with clamshell T/Rs.

Matt said...

I work for a Canadian operator of B737-200s. Our MEL has no mention of any slippery rwy limitations.

Aluwings said...

Thanks for this information.

I think there's a hierarchy from the Manufacturer's MMEL down to the Regulatory Authorities, down to what our company called the MEL (just one M - dropping the word "Master" from Master Minimum Equipment List).

I suspect that the manufacturer produces as simple and flexible a document as possible which only deals with safety-related issues. Then the Regulators may decide to add something - such as no ops on standing water. Then the individual carrier might add further restrictions for their own operation.

Our company-specific manual includes some passenger comfort items such as guidelines for the number of operating lavatories for short and longer haul flights vs. the number of passengers. I don't think a manufacturer would bother to include that.

jetdrvr said...

Apples and oranges...A B-737 MEL has no relationship to an A-319 MEL, except in name, only. They are two conceptually totally different aircraft.

If you want to comment on the A-319, then publish the page from TAM's MEL. That is the only document that is pertinent.

Aluwings said...

Hey Jetdrvr, thanks for the comment. My post isn't specifically about TAM but rather about the differences that exist in MELs, and why that might be. I was wondering why what is kosher in one company's or country's operation may not be so in another's. Each MEL is specific not only to the aircraft type, but also to the regulatory body and the airline.

Apparently it was legal for TAM to operate into that airport on a "flooded" runway, so that's a reflection of how their particular MEL is worded. And it's interesting to see that some MELs for identical aircraft can be more conservative than others.

Hermenauta said...

Sorry but this is the letter of the FAA MMEL considering Thrust Reverse Systems (page 280):

"M)(O)One may be inoperative provided:

a) Inoperative reverser is deactivated and secured in the stowed position, and no operations or procedures require its use,
b) All stow and deploy switches on the inoperative reverser operate normally (CFM only),
c) REV PRESSURIZED caution is not present on ECAM,
d) Wheel brake tachometers operate normally, and
e) Main wheel braking system operates normally."

So it seems it's not true that the MEL states that "you can only dispatch with an inop reverser if the other reverser is disabled." _ as long I understand what the MMEL says.

Aviatrix said...

And the joyous part is the interdependence of the various MELable items, so that you might know by heart from experience that you can dispatch with one fuel flow gauge and with an inoperative back up fuel transfer pump, but you still have to check the manual to ensure they can be both u/s at the same time, at night, on a Tuesday, when the FO has the middle initial L.

Anonymous said...

Yep, Aviatrix. Been there for sure. I wonder how complex things might get before we reach that point of diminishing returns... where it's not worth the effort.

At my airline the rules surrounding alternate airport fuel has become so complex that a long "decision table" was developed to help the pilot step through the process. All to shave more fuel off the flight plan while maintaining the desired safety level.

Add in the "approach ban" rules, and a dozen other such items and it gets so the Captain needs a new crew-member - a legal advisor to figure this stuff out.

Or at least a 1-800-"callmylawyer" number on the flight deck... I can hear a typical coming across the line now:

"Yes, Hello - legal department? Ah, we're currently circling over KEWR where the weather is XYZ. The last 1,000 feet of the CAT2 approach lights just went u/s, but our landing table says we dont' need that much runway. We're operating as a Canadian carrier in U.S. airspace so does our operating certificate allow us to utilize the Canadian "look see" rule because the tower just reported a vis. of XYZ2. Meanwhile, if we need to hold longer could we shorten our alternate to (name an airport) where the new forecast shows XYZ3 but the ILS approach is slated to go off the air at ZZ:ZZ Zulu... Oh yes, did I mention that we have an MEL item no. 30-XX-XX, and it's been in the book 10 days and we have just turned the clock into the 11the day zulu - or does local time dictate? I can never recall - so the aircraft may be grounded upon arrival - So, to get to the point, should we continue to hold, do the approach or just return to airport of origin? And please hurry up with the answer as our min. fuel 'Bingo' time is approaching rapidly with our existing alternate - which by the way is showing deteriorating weather. ... Hello? Hello? Anyone there?" ... buzzzzzzz .....

Anonymous said...

"The last 1,000 feet of the CAT2 approach lights just went u/s,"

Oops - I meant "CAT2 center line lights" ... sorry..

moe said...

some new light:

http://www.latimes.com/news/printedition/asection/la-fg-brazil2aug02,1,3285208.story?coll=la-news-a_section

Anonymous said...

Still pretty vague... I wonder what they mean by "throttle in the wrong position." Not selected to reverse? But if the reverser is deactivated, what does that mean?

And the comments about the slippery runway no longer being a factor sounds ridiculous. Could someone be trying to cover their backside?

There have been accidents with the Airbus in the past where reverse and ground spoilers failed to extend after landing because the weight on wheels switch and the wheel-spin signal both failed - (too soft a landing on a wet runway as I recall).