Flight on 737-800

[frequentflyer2]

Once again this is a genuine question and not intended to level criticism at any member of Ryanair's flight crew. I'm just curious to find out what procedures were being followed.
Mrs. FF and I took off from Stansted tonight on a Ryanair 737-800 on our way back to BHD.
Initially, the aircraft was climbing powerfully. Then the engine note changed as it made a turn. It then really seemed to die away and the aircraft or some part of it was vibrating.
Eventually it began to climb again as the amount of power was increased.
I know these aircraft do seem to vibrate at times but this was so noticeable Mrs. FF feared the reduction in power was too great putting the plane in danger of stalling.
She wasn't the only passenger who sat up and took notice.
What was happening and what causes the vibration on this type of aircraft?
If a noticeable reduction in power is going to occur immediately after take-off wouldn't it be a good idea for pilots of any airline to mention this to passengers when welcoming them on board?
This really could help calm some genuine fears.

[Flight Detent]

Maybe they will do better at remembering the flap maximum speeds next time!

[Northbeach]

It is always a challenge to comment intelligently or offer an accurate analysis on an event that I did not witness.

“Initially, the aircraft was climbing powerfully.” You and I know this is normal, so far so good.

“Then the engine note changed as it made a turn.” By “engine note” I presume you mean the volume and intensity of the exhaust noises. Normally the thrust demanded of the engine is reduced after takeoff and the jet is at some predetermined altitude above the airport. That is done to extend the life of the engine and for economy. This power reduction may or may not coincide with a turn, but the turn in and of itself likely had nothing to do with the change in noise level.

What may have happened, pure speculation on my part, is the crew was commanded by air traffic control to immediately stop their climb and turn to a different heading to avoid some potential traffic conflict that was not anticipated earlier by the air traffic controller. Or the pilots may have done an evasive maneuver on their own to miss another airplane: power back immediately to stop the climb, slow the closure rate to the threat and turn away from the traffic.

“It then really seemed to die away and the aircraft or some part of it was vibrating.
Eventually it began to climb again as the amount of power was increased.” The vibration could have been the turbulence generated by another passing airplane (wake turbulence). That would fit the scenario of the airplane being told to stop climbing and turn to a different heading.

“If a noticeable reduction in power is going to occur immediately after take-off wouldn't it be a good idea for pilots of any airline to mention this to passengers when welcoming them on board?” It is very possible that your flight crew had no idea this event was going to take place immediately after take off. Therefore it would have been impossible for them to forewarn you prior to takeoff.

“This really could help calm some genuine fears.” Your perception is your reality; what was genuinely frightening for you may have been completely routine for your pilots. I recognize you mentioned other passengers acknowledging the strange circumstances by sitting up to take notice. Or, it is possible the crew pulled the power off and the airspeed did decay to the point where the airplane began a slow speed buffet, approach to a stalled condition. This is a dangerous position to be in. And it is a possibility that your flight was in just such a precarious position.

Whatever your circumstances your pilots did not make an announcement either because they did not know what to say and were not comfortable with their circumstances or they did not believe anything out of the ordinary had happened. I was not there and I do not know.

When you have a question like this you can always ask the crew after the flight. I would recommend asking the cabin crew to let the aircraft commander know that you have a question related to the flight that you would like to ask. Be as respectful, non-threatening and as private as possible; under those conditions ask the Captain to explain the circumstances that have you concerned. As long as the Captain doesn’t feel threatened (professionally) you should get an honest answer. Not everybody (flight crew) will respond well or tell you the truth, but I imagine the majority would (cultural differences noted). After all you are the paying passenger. If you don’t like the way you are treated and/or the answers or explanations you can always write a letter to the company-eventually it will get back to the crew. Your money talks very loudly and is clearly heard by airline management types.


Respectfully,

[frequentflyer2]

Oh thank goodness not to be told 'don't be silly the pilots know what they're doing' etc.
I've flown many times and this just didn't feel normal.
I was sitting in the aisle and Mrs FF in the middle but once the doors were closed she moved to the window to enjoy the view as it was a beautiful evening.
I was relaxing with my eyes closed as the aircraft made its initial climb but what felt like a loss of power brought me back into full consciousness. I pretended to still be asleep because I didn't want to say 'this doesn't feel right'.
Mrs FF says the only way she can describe it is to say it banked about three times to do a U turn and seemed to climb at the same time as if it was climbing a staircase, with power increasing and decreasing several times.
The vibration I'm talking about was the same as I would expect on this aircraft during descent - a sort of slight juddering motion - and it just didn't feel right at that stage in the flight.
I know for example when climbing out of Heathrow planes will level off with a reduction in power and then climb again with an increase in power.
But last night's flight just didn't feel normal.

[eliptic]

frequentflyer2 (http://www.pprune.org/members/131554-frequentflyer2)

What you describe(if i got it right) i did experienced if not many but close to

It feels like the A/C will fall down,,:eek:

[Dit]

It may well be part of a departure routing that includes stepped climbes (like the staircase you mentioned). The proceedure in RYR is to select VNAV to climb, which wil command full thrust from the autothrottles and then use the pitch to control the speed, it will do this even for steps of 1000 feet. I know from experience that the noise reduction in going from full thrust to the thrust required to maintain straight and level 220 kts can make it sound like the engines have stopped! The engines also produce small vibrations at certain power settings, however its nothing pronounced.

When you have a question like this you can always ask the crew after the flight. I would recommend asking the cabin crew to let the aircraft commander know that you have a question related to the flight that you would like to ask.
Agreed...

We can't forewarn you of everything you might pick up on that sounds or feel 'abnormal' when it almost certainly isn't. Plus I believe doing so would probably only make the situation seem worse for the majority of the passengers.

[rafo26]

Aircraft engines are to be only at take off power for about 5 minutes,otherwise there will be far to much pressure on the engine operating at this speed,the throttle was just taken back a little as the aircraft had generated enough airspeed to continue the climb.As for the unusual vibration,wake turbulence or maybe a boat fairing on the flaps a little loose,nothing to be worried about however

[victorc10]

You wouldn't be using VNAV if you were step climbing out of Stansted.. VNAV just means the computer is controlling the Autopilot rather than the pilot. For those who are not pilots.

Some engines do vibrate a little and can cause what some passengers might consider unusual noises and or vibrations, especially if both of the engines are vibrating at different frequencies. Some can vibrate more at high power settings, others more at intermediate settings. I wouldn't have thought it was anything to do with flaps or wake.

V

[Dit]

Why wouldn't you be using VNAV? I would, especially as it is the companies preferred Vertical Navigation mode. It covers you're behind in case of a altitude constraint on a SID, and if you get a climb from the controller,simply hit the ALT INT button a few times, it takes out all the altitude constraints and pretty much becomes the same as LVL CHG.

Again, why not VNAV?

[victorc10]

Depends on the size of the step, I had in mind less than 3-4K'. Just from my own experience out of Stansted.

[piton]

Dit,

Many 737NG's do not have ALT INT (or SPD INT). We have a full NG fleet and only recently started installing that option. With "old fashioned" VNAV the use of vertical speed climb is much smoother for small (couple thousand feet) changes in altitude (also less chance of setting off TCAS in crowded airspace). Use of VNAV without altitude intervention gives a large power increase and pitch change plus the restraints remain in the FMC.

[Final 3 Greens]

FF2

As another frequent flyer, I am constantly surprised by the different noise and vibration levels experienced.

e.g. this week I flew easyJet from Gatwick to Madrid and then from Madrid to Gatwick a couple of days later. (Good service both ways, I do think U2 have a pretty good product these days and their cabin crew are generally excellent.)

Both aircraft were A319, I assume with the same engine spec.

I sat in the same seat row, both ways.

Going out, the engines 'felt' smooth (obviously there is no vibration instrument available for pax), but coming back, rough and noisy. Obviously I don't know what weight each aircraft was carrying and what power settngs were used.

I suppose that every engine is built to a tolerance (so thre is some slight variation due to common causes) and as pax we encounter them at different stages in their operational lifecycle (therefore possibly increasing the variation), so one can experience different sensations even when the pilots manage the power in the same way.

I used to fly a small fleet of light aircraft, same airframe, same engine spec and there was a considerable difference between these as well.

[Musket90]

The STN-BHD departure route off runway 23 I think is limited to 3000ft initially to avoid conflict with LTN traffic, then step climb depending on ATC. So quite normal for engine power to significantly reduce soon after take-off on this routeing and before the right turn around the town of Bishops Stortford. Also there is noise monitor limits to adhere to.

[Dit]

Piton:
Granted other airlines may not have the ALT INT button, but al of our a/c do (being as ff2 refered to an FR flight). I do agree that small steps can be better managed in V/S, however our proceedure is to engage VNAV (using ALT INT to delete any altitude constraints no longer required), then change to V/S 2000fpm (if req) at 2000' to go and V/S 1000fpm (again if req)at 1000' to go.

I'm led to believe that doing all climbs (even 1000' or so) at CLB thrust should be more fuel efficient than V/S climbs, however, I reserve the right to be mistaken!

I wrongly assumed victorc10 was an FR pilot and was trying to point out a mistake in my arguement.

[frequentflyer2]

Thank you all for taking the time to answer my query.
It's been very reassuring. The vibration I referred was a sensation I've experienced on 737's before but during descent not climb.
I've taken off from Stansted a number of times but normally in the opposite direction. Perhaps this had a bearing on the manner in which the pilot had to fly the aircraft.
Anyway, it would seem everything was quite normal so neither Mrs. FF or I will be startled if we experience the same noise and attitude changes again.

[doncas]

Hi All,

Just to give an insight in to engine vibration...

There are operating limits for the amount of vibration an engine can produce before maintenance action is required.

For a Boeing 737NG (CFM56-7 Engine) The limit is approximately 4 MILS (or 0.004") A very high tolerance... Most airlines will keep this value much less than this, at around 1 MIL. If it approaches 3 MILS, maintenance action such as fan balancing or fan lubrication is carried out as any vibration can be uncomfortable for the passengers and crew. There are vibration sensors on both engines to detect this.

There is also a phenomenon of natural frequency of the fans, and a 'sweet point' at which both engines cause mutual vibration on one another. Several factors play a part in this, but fan speed is the main player. This will normally occur at high fan speeds (above 90%). This dies out fairly rapidly, usually when the thrust setting is changed, or the pitch of the aircraft changes.



So, hopefully this will shed a little light on where the vibrations come from, and hopefully reassure the fliers out there that slight engine vibration at certain stages of flight is normal, and is monitored to ensure it doesn't increase to the point of causing any sort of damage to the aircraft!

Regards
D

[Desert Diner]

The vibration could have been the turbulence generated by another passing airplane (wake turbulence).

Turbulence will not make a plane not vibrate but shake.

[pilotmike]

On a departure from Stansted RW23 to Belfast, they would fly a BUZAD6 ROMEO departure.

After climbing on close to full power to flap retraction altitude, they would reduce power whilst lowering the pitch attitude significantly, and retract the flaps, before continuing the climb to 3000' and making a right turn at 3.1 Nautical miles, whilst maintaining a speed of no more than about 220 kts to stop them from going wide on the turn and triggering a noise violation, changing from Tower on 123.8 to Director on 136.5 (was 126.95 until last week), and identing the squawk on transfer to Director - all of these simultaneously on that departure usually. The turn would continue to 352 degrees inbound on the BKY 172 degree radial, with subsequent climb as instructed by air traffic, usually to Flight Level 70, with a left turn outbound BYK on 265 radial unless instructed otherwise by air traffic, all whilst accelerating up to the limit of 250 kts below FL100.

The pilot flying would have briefed all this to the pilot not flying before departure, along with specific points pertinent to that specific take off, including reviewing emergency procedures etc. However, with the limited time in the turnaround, they would not have had time to deliver the same departure brief to the passengers. Nor indeed would the passengers have fully understood it. Nor indeed would many (if any) be interested.

[eliptic]

doncas (http://www.pprune.org/members/128108-doncas)

I have a question for you :)

Quite many times i have heard a "metallic sound" from the engines (that follow the rpm) especially on the 777.
It sounds like the fan blades hits the outer edges ,,whats that sound?

Ps thanks for the "vibration answer" Ds