Northwest Jet Suffers Similar Malfunctions to Air France Flight

Wall Street Journal ^ | 26 June 2009 | ANDY PASZTOR and DANIEL MICHAELS

[Erik Latranyi]

A Northwest Airlines jet traveling from Hong Kong to Tokyo last Tuesday suffered a series of equipment and computer malfunctions strikingly similar to those encountered by Air France Flight 447 just before it crashed into the Atlantic Ocean on May 31.

The Northwest plane and its passengers, however, emerged unscathed. Details of the harrowing incident – described in a memo by one of the Northwest pilots and confirmed Friday by others familiar with the matter – highlight how cockpit crews can safely cope with something that is almost never supposed to happen: a system breakdown that prevented the crew from knowing how fast the plane was flying.

During the brief but dramatic event, the Northwest Airbus A330's crew was left without reliable speed measurements for three minutes. In addition, the computer safeguards designed to keep the aircraft from flying dangerously too fast or too slow were also impaired. Like the Air France A330 jetliner, the Northwest plane entered a storm and quickly started showing erroneous and unreliable airspeed readings.

[50mm]

I’m lost on why determination of air speed should be a problem then

Think of it this way: If your ground speed is 200 mph, but you have a 100 mph tail wind, then your actual air speed is only 100 mph (200 mph - 100mph). If you have a 100 mph head wind, then your air speed is 300 mph with a 200 mph ground speed. The aircraft doesn't care what the ground speed is, only the speed of the airflow past the aircraft.

[safisoft]

Composite is indeed an issue... but not the way your "expert" intends. Like any new technology, it should be carefully considered before implementation. However, does your "expert" know how much composite is used in the still-grounded Boeing 787? How about the C-17, F-22, and F-35. And being Brazilian, surely he must know how much it is used in his own country's Embraer E-170 and E-190?

This stuff reminds me of the Luddites.

[magellan]

And there's the key - the A330 was still working properly.

I wouldn't define a possible failure of multiple pitot-static and/or air data systems as "still working properly". It is like saying a car without brakes or a steering wheel still operates normally because it can propel itself.

Fortunately, the airplane's engine control systems continued to work, allowing the pilot to control the speed of the airplane using power settings.

The pilot said the airspeed indicators returned to normal, but the flight-control computers never did.

The question is, was this caused by some kind of pitot-static system issue (i.e., icing), or an air data computer issue, or some combination of both.

I am guessing it is a pitot-static icing problem which introduces out of norm data into the air data system, which given the flight conditions (high-altitude, high speed cruise) causes the air data computer to go haywire.

[gusopol3]

So the airplane makes its own throttle adjustment to the airspeed data ? Sounds like the DC metro train unfortunately.

[Vaduz]

Every ststem on this aircraft is fail safe fail safe fail safe.Fly by wire die by wire.

[bert]

My friend is a pilot, not a structural guy. The report was attributed to George Larson, Editor emeritus of Smithsonian Air & Space Magazine.

[gusopol3]

so airspeed is a quantity relative to the surrounding atmosphere rather than to GPS coordinates; thank you.

[ops33]

GPS will tell you your ground speed, it will not tell you your airspeed.

[ErnBatavia]

GPS on Tomtom

Having had no experience with such gear, we bought one in early May for our recent month toodling around the lower third of the entire country....amazing what these little gadgets can do.

[patton]

Air moves. Your GPS indicated speed will enable you to crash very accurately.

[reg45]

Airspeed is the primary factor in causing lift. If flight were not totally dependent upon lift, then air speed would be unimportant.

[reg45]

NTSB should ground all A330’s until this problem has been fixed.

[gusopol3]

ours got stolen; consequently spent 45 minutes looking for a pizza shop last night rather than 10 minutes.

[safisoft]

Think of it this way: If your ground speed is 200 mph, but you have a 100 mph tail wind, then your actual air speed is only 100 mph (200 mph - 100mph). If you have a 100 mph head wind, then your air speed is 300 mph with a 200 mph ground speed. The aircraft doesn't care what the ground speed is, only the speed of the airflow past the aircraft.

Ground speed has nothing to do with it. Once a part of the moving airmass, tailwind/headwind have no effect on the airflow over the wing. The real issue is that airspeed is a function of the density of the air, and as you climb into thinner air, your INDICATED airspeed is quite different from your TRUE airspeed (ground speed means nothing to an airfoil). For example, at 35,000' in standard conditions (15c, 29.92, standard deviation) 240 knots INDICATED airspeed translates into 450 knots TRUE airspeed. It is that efficiency that makes modern airliners work. There are other issues such as outside air temperature and compressibility (as air is compressed going over the wing, the temperature rises as does the air density).

Since the all the WING cares about is INDICATED airspeed (the real effect of the molecules moving over the wing), knowing what the INDICATED airspeed is at any given moment is vital to an airliner at high altitude, because the maximum mach number and the minimum airspeed are VERY close the higher you climb.

At 41,000 feet, on most subsonic aircraft, max mach and minimum airspeed can be within 10 knots of each other, and you fly between the two (called "coffin corner" to us old-timers). In other words, speed up 5 knots, the aircraft starts mach buffet and possibly comes apart - slow down 5 knots and the aircraft goes into aerodynamic stall, and plummets, at an altitude that makes recovery difficult if not impossible.

[magellan]

Found this on another forum. It is the pilot's report of the event:

"Tuesday 23rd June, 2009 10am enroute HKG to NRT. Entering Narita Japan airspace.

"FL390 mostly clear with occasional isolated areas of rain, clouds tops about FL410. "Outside air temperature was -50C TAT -21C (you're not supposed to get liquid water at these temps). We did.

"As we were following other aircraft along our route. We approached a large area of rain below us. Tilting the weather radar down we could see the heavy rain below, displayed in red. At our altitude the radar indicated green or light precipitation, most likely ice crystals we thought.

"Entering the cloud tops we experienced just light to moderate turbulence. (The winds were around 30kts at altitude.) After about 15 seconds we encountered moderate rain. We thought it odd to have rain streaming up the windshield at this altitude and the sound of the plane getting pelted like an aluminum garage door. It got very warm and humid in the cockpit all of a sudden. Five seconds later the Captain's, First Officer's, and standby airspeed indicators rolled back to 60kts. The auto pilot and auto throttles disengaged. The Master Warning and Master Caution flashed, and the sounds of chirps and clicks letting us know these things were happening.

"Jerry Staab, the Capt. hand flew the plane on the shortest vector out of the rain. The airspeed indicators briefly came back but failed again. The failure lasted for THREE minutes. We flew the recommended 83%N1 power setting. When the airspeed indicators came back we were within 5 knots of our desired speed. Everything returned to normal except for the computer logic controlling the plane. (We were in alternate law for the rest of the flight.)

"We had good conditions for the failure; daylight, we were rested, relatively small area, and light turbulence. I think it could have been much worse. Jerry did a great job flying and staying cool. We did our procedures called dispatch and maintenance on the SAT COM and landed in Narita. That's it."

Warm rain at FL390. I bet there was a hailstorm down on the ocean below.

[safisoft]

NTSB should ground all A330’s until this problem has been fixed.

Exactly what "problem" is that? Instrumentation fails on some airliner somewhere multiple times every day, and the crew handles it exactly like this crew did... a non-event. No one knows WHAT happened to the Air France aircraft. If the FAA grounded aircraft as you suggest, the industry would cease to operate, and never get off the ground. Pilots are trained to deal with anomolies, and we deal with them REGULARLY.

[em2vn]

Geez I hate to post this but here goes. It’s like NASCAR drivers establishing their pit road speed by the rpms shown on the tachometer in a specific gear.
I’ve driven a car with a broken speedometer but a functioning tachometer. I determined speed by rpm readings and the gear I was in from prior experience in the car.

[safisoft]

Fly by wire die by wire.

Which begs the question why every aircraft designed after 1994 (military and civilian) is FBW? Those stupid aircraft designers, don't they know that HYDRAULICS and PIANO WIRE ACTUATION is much more reliable! /sarc. Sheesh.

[gusopol3]

I think this is why I was never much good at flying a kite; my only solution ever to be was “run faster.”

[redgolum]

Sounds like the pito (spelling) tubes need better heating.