4
$\begingroup$

This question is based on this episode of Air Crash Investigation concerning crash of Lauda Air flight 004.

It discusses a test flight that simulates the crashed flight (41 minutes and 20 seconds into the video), in order to determine the effects of a sudden unintended reverse thrust deployment at higher altitudes and speeds, than those of the original test flight (which tested the deployment with the Boeing 767 at around 10,000 feet).

However, since there seemed no preventives or recourses for this test flight, was this test flight as dangerous and likely to crash as Lauda Air Flight 004? If so, was it a forlorn hope or suicide mission?

ACI did mention that this test flight was conducted with the 4-engined DC-8, instead of the 2-engined B767, so is ACI implying that the greater number of engines on the DC-8 was a corrective?

$\endgroup$
1
  • $\begingroup$ "ACI did mention that this test flight was conducted with the 4-engined DC-8, instead of the 2-engined B767, so is ACI implying that the greater number of engines on the DC-8 was a corrective?" — Can you rephrase this? I can't, for the life of me, figure out what's meant. $\endgroup$
    – egid
    Jan 20 '15 at 3:38
11
$\begingroup$

The test was flown on a DC-8-72. This model aircraft is certified to have its inboard thrust reversers deployed during flight, which means that the test was either within standard operational guidelines or not too far outside them (it's possible it's not supposed to have reversers deployed at Mach 0.8, but it's allowed to have them deployed at speeds over 190 knots per @UnrecognizedFallingObject's comment, thrust reversers are allowed up to Mmo). In addition, both inboard thrust reversers were deployed; the TV show is wrong when they claim that there were 3 normal engines and one reversed one. As the test found, there was some buffeting, but there wasn't the need for too much lateral control input, because of the symmetry (there was a bit of asymmetry when deploying reverse thrust, but not once both were deployed). Also, crucially, the flight crew was prepared for this, and they had the outboard engines fully spooled up (so while there was high sink rate at high speed, they had the power to come out of the dive safely). The test protocol had them maintaining airspeed, idling the reverse thrust engines before the end of the reverse thrust run, and then having engines at full thrust already to pull up.

In short, the reason it wasn't a suicide flight was that the flight crew was prepared, the plane could take some degree of reverse thrust in flight, the reverse thrust was symmetric, the outboard engines were both spooled up and pitch was adjusted to maintain airspeed, and in general it was a controlled test environment. The TV show implies it was to see if it was possible to recover. That was not the purpose of the test; they set up the test so they knew they could recover, and the purpose was to see the effect on airflow over the wing in as controlled an environment as possible.

Source: NASA report on the test flight

$\endgroup$
1
  • $\begingroup$ On the DC-8, it is allowed to deploy the inboard reversers in cruise up to Mmo -- in fact, it is SOP to do so if an emergency descent is needed. Source $\endgroup$ Feb 25 '15 at 3:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.