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I just finished watching National Geographic's Megafactories: Boeing 747-8.

During the test flights, a bunch of engineers are on board the plane, presumably controlling the water tanks that distribute weight, and collecting the data.

Another time I'd seen it was when they were testing detection systems for microbursts. There were about a dozen engineers sitting on the plane, watching monitors while the crew deliberately flew into hazardous conditions.

Why do they risk the safety of these engineers, when presumably the work they're doing could be automated or controlled remotely? For data to be observed, couldn't they do that from the ground?

Is this a case of "we've always done it this way?" Even now that we probably have the technology that would allow the engineers to avoid having to go on test flights, I'm guessing that changing this procedure would be a lengthy and difficult process.

Besides the pilots, why does anyone else need to be on board?

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    $\begingroup$ :) If I'm not mistaken, in the past the "engineers" would be the first to cross the bridge they've just built :D $\endgroup$ – woliveirajr Jun 6 '14 at 19:10
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    $\begingroup$ Who claims that the engineers "need" to be on board? $\endgroup$ – user2168 Jun 8 '14 at 23:44
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    $\begingroup$ Skin in the game -> better aircraft design. $\endgroup$ – davidbak Dec 13 '18 at 22:28
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More and more data is collected in flight testing of aircraft. While 50 years ago they might have only designed for a small number of scenarios, the advances in computing allow them to design modern aircraft for thousands of scenarios. Modern certification standards include more and more requirements, which include flight testing for many of these requirements.

While some information is sent to the ground (like in this video), other information may not be. Airplanes in flight test have sensors for temperature, pressure, stress, and many other parameters located throughout the plane. These generate a lot of data, more than may be practical to send on a live data link. There may be several reasons that the engineers would want to analyze a lot of information onboard.

Some of the tests need to have multiple parameters coordinated with the pilots. If they are flight testing stall, for instance, they need to be sure they have flight parameters are correct for that test. The engineers give the pilots guidance on getting the airplane into the right configuration. The engineers also verify that the the information they collect is sufficient for the needs of the test. It's much more expensive to come back and realize they didn't get what they needed and must go back up to re-run the test.

Some of the data is also critical for safety. One subject of the tests is flutter. Flutter conditions can be very dangerous to the aircraft. The engineers help monitor the data and make sure that things don't get out of hand. If a data link were to be interrupted in a case like this, safety could be compromised.

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In a perfect world, you wouldn't need the pilots as well...

To your question:

  1. No modern instrument can currently match the feeling of "just being there".
  2. Data recorded on the plane and transmitted to the tower is lagging or even impossible to collect live (due to technical difficulties).
  3. Flying takes a lot of attention from the pilot. Even if they're good engineers (besides being a pilot), you wouldn't want to waste an experiment.
  4. Engineers don't go to preliminary (dangerous) flight test.
  5. Some engineers enjoy being on board the machine they designed.
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    $\begingroup$ how much is the realtime delay in data collection? $\endgroup$ – shortstheory Jun 6 '14 at 13:18
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    $\begingroup$ Commonly, a few (<5) seconds are accumulated. $\endgroup$ – Sparkler Jun 6 '14 at 13:29
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    $\begingroup$ I would also question the implications of answer 4. By making that statement, you are implying that the flights engineers do go on are not dangerous. If they are moving large quantities of water weight on board, affecting the CG, and recording the effects of the changed CG, it seems that that flight may be (just as) dangerous. Also asnwer 1 is subjective, and an engineer aboard is not likely there for subjective 'feelings'. $\endgroup$ – CGCampbell Jun 6 '14 at 14:24
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    $\begingroup$ this is a bit off-topic, but engineers who participate in policy-making in their organization, are expected to be biased towards requiring engineers on board. $\endgroup$ – Sparkler Jun 6 '14 at 15:02
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    $\begingroup$ I'd also add that they are there just in case there is something wrong with the equipment or software and the data isn't being recorded correctly. It would be bad to waste an entire (very expensive) flight because data wasn't being recorded correctly, especially if it could have been fixed without cancelling the flight. $\endgroup$ – Lnafziger Jun 6 '14 at 15:36
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Usually, engineers on board on the aircraft serve the same purpose as engineers in a control room. (The control room for space missions in Houston is probably the best, most widely known example of a control room.)

Having the engineers on board reduces the need to send the data to the ground via telemetry (TM), which may be a necessity based on limited bandwith, etc. A description and illustration of the control room and its purpose appear here.

It also allows for better coordination amongst the crew, as the pilots, who need information that the engineers are monitoring, can discuss more effectively with the engineers when they are on intercom.

Flight Test Enginners (FTEs) are another kind of engineer on board the aircraft, and they specialize in test conduct. They are present to guide the test pilot, assist in determining if the maneuver was flown correctly, evaluate data quality, and make decisions about whether to continue testing.

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  • $\begingroup$ Hi Mark. Just a heads up, here: I see you have linked a fair bit to multiplyleadership.com in your answers. While links to external resources to add to your answers (as opposed to the link being the primary content in the answer) can absolutely be beneficial, you should take care to ensure that this is not construed as spamming. See How to not be a spammer in the help center for further discussion on this. $\endgroup$ – a CVn Jan 1 '18 at 15:55

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