737 NG Ground Run Max N1 before skidding.

[asteroid01]

If post maintenance work requires a 100% N1 ground run, can it be done against the brakes or will an empty 737NG begin to skid before 100%N1? Obviously it depends on surface friction and weight but let's assume the surface is dry/Good and that the machine is empty due to still being under maintenance.

I know the answer is in excess of 70% because the similar, but unrelated, Supplementary Procedure for preventing ice build up on the ground requires, if possible, a MINIMUM of 70%.

And are there any other considerations like compressor stall possible? I know that the surface is important (Google "NL B734 Damaged During Engine Run Up" which gives a link to airliners.net...........Shaheen ended up with a patio on their stabiliser!)

Are there any engineers out there that have been trained for ground runs that can help with this query?

The question arises following a tech issue at an outstation when I had to do a full rated thrust ground run after maintenance work.

[Dufo]

You don't need to run all engines at required power at the same time.
70% N1 is nowhere near 70% of power, more likely around 40.

[asteroid01]

That is a very interesting thought. I had not considered ground running the engine in question upto max while the other remained at idle.

I know there are ground run courses for engineers..........has anyone been on one?

[tdracer]

Haven't worked the NG, but on the wide bodies the procedure is to set the opposite engine to ~70% N1 to limit the side torque on the nose gear before running the test engine to a climb or TO power setting. There are also minimum fuel loads required prior to running to high power.

However most 'high power' engine tests no longer go to full takeoff power - with FADEC we've been able to use something around max climb for most 'high power' testing.

[munster]

The maintenance manual will specify a minimum fuel load, the heavier the better.
There will be tables showing appropriate take of power values according to the local air pressure and OAT.
It's better to use some balancing power on the other engine to reduce the tendency to twist. Position the aircraft into wind, fully chocked and you'll be fine.

[AeroStadt Aviation]

What Munster said ^^^

After flying the 737NG (800) for 8-years in a Part 91 PU/121 Supp operation where we as the small group of line pilots did the post-mx acceptance along side our flight mechanic... we always had a maintenance procedure available to us. Our static engine runs were never to 100% N1 though, and we typically brought the opposite engine up to an intermediate thrust setting to reduce side-load. I'd really recommend digging it out of the MX procedures to avoid an embarrassing episode.

[boeing_eng]

For high-power runs on the NG, full-wings is the recommended fuel-load at my company.

All engineers who run airliner sized engines "should" have specific training (usually on a simulator) and be approved by their company. If a pilot is expected to carry out a post-maintenance engine runs, (in the absence of suitable engineer) I would advise seeking the advice of the company Maintrol dept (or a qualified engineer) who should be able provide guidance etc.

[asteroid01]

Can I ask if anyone would ever advocate a ground run being performed via a very low speed reject when performed by the pilots at an outstation? i.e. Immediately after the aircraft began to roll.

This is the procedure we used at an outstation and I was somewhat gobsmacked when I was told during the taxi out that the brakes would be released then the TOGA button pushed before an immediate reject performed. The objective was to test if maintenance work had fixed and would prevent re-illumination of the COWL ANTI-ICE annunciatior (due faulty valve / over pressure from 9th stage) when Takeoff thrust was set............previous day we had this condition, rejected and then stopped for the night.

I would have expected simply to apply Takeoff thrust against the brakes as opposed to performing the low speed reject. Was the low speed reject inappropriate? Could we have done this without brake release?

[boeing_eng]

The question should be how can the maintenance staff who carried out the work certify that it had been tested prior to releasing the aircraft for service?

If the work had been carried out correctly and fully tested there would be no need for the test. If you were carrying out the test at the request of an engineer, I assume if the test was successful the engineer would then certify to that effect prior to releasing the aircraft??

[asteroid01]

I was considerably unhappy with my colleagues decision to release the brakes during the test and wanted to know if takeoff thrust could be set against the brakes.....were the brakes capable of holding the aircraft stationary?

[NSEU]

My former airline used specially designed chocks for full power engine runs. Aircraft tend to squirm around on the tyres with full thrust/brakes applied. I wouldn't even rely on normal wooden/plastic chocks, let alone brakes. Anecdotal, but I've even heard of a 747 nose moving 6 feet sideways after an engine stall.

[Centaurus]

I recall that the Mustang had a long steel tube that could be slid through a hole in the fuselage near the tail plane and tied to the ground for high power runs.

Should be simple enough for a 737 to open both rear exits - put a seriously strong steel bar between them and have a chain attached to each end leading to steel tie down hooks into buried concrete blocks either side of the fuselage. Then open up to 40% N1 for even stabilisation and hit TOGA.

[grounded27]

We are not reinventing the wheel here. For modern jet era aircraft, the procedure has never changed. Minimum fuel, 60-70 as prescribed % N1 opposite engine to required thrust. I have as well heard of a 747 swinging the nose if 1 or 4 coughed, I suppose the same issue exists with the A340. None the less, A 2nd person for safety should always be standing on the brakes as well, brakes can usually be set but pedals must be occupied by both people. Pre FADEC motors, this was usually done to adjust the fuel control or verify proper power could be achieved.

[cosmo kramer]

asteroid01, why were you unhappy with letting it roll and subsequently doing a low speed stop?

What was your worry? I could understand if it was an engine problem, but since you say it was to test a cowl anti-ice valve, I can't think of anything that would make said procedure unsafe or even a slight risk. Rather I would say it sounds a lot more controllable than a static run again takeoff thrust.