Rough runway

[Vaneev]

Sometimes I have to fly from rather rough runway. I am interesting if Boeing 737 has limitations as to jogging during takeoff and landing roll and taxi? May be in the form of range of allowable load factor during ground operations? I think that nose gear suffer the most and it is useful in that case to unload nose gear during takeoff roll prior Vr. I'd be grateful if you can share your experiences with me. Thanks in advance for your time and knowledge. Safe flight.

[Rainboe]

Runways are checked for performance and roughness. if the runway is cleared for operations, you may assume it is considered acceptable. Flight recorders will start picking up excessively rough runways for attention.

There is no special rough runway technique. You should not try and lift the nosewheel, nor should you hold the stick nose down- just let the stick go in the neutral position until rotate.

[SNS3Guppy]

Khabarovsk in Russia has seen improvements, but has resulted in wheel changes on more than a few occasions following a landing there. When it comes to a tech stop for fuel along that route, it's one of the only games in town,though.

I don't go there in a 737, however, so can't comment on operations in that type. We don't review our FDR data for landings in UHHH...we just go in there for fuel, and know that it's a less than perfect runway.

Battle Mountain in the US used to take big chunks out of our tires when operating 4Y's in the summer. Cost of doing business.

[tcas1]

When operating from rough rwys my company has a policy where a greater flap setting is used to reduce the ground run. This is on a 737-800.

[krujje]

Taxi on rough runways is a certification requirement for transport category aircraft. The criteria is "the roughest ground that may reasonably be expected in normal operation". You can check FAA advisory circular AC25.491-1 for details on what is done to certify aircraft for these conditions. One of the standards for this was the so-called San Francisco runway, which was apparently quite rough until it was re-paved... but I know some manufacturers have taken to using roughness data from a runway in Russia, although I don't know which one exactly. Flight data recorders may not be totally accurate for quantifying runway roughness, as many of the dedicated FDR accelerometers installed on aircraft attenuate frequency content above 4 Hz.

[Sir George Cayley]

Have a look at myboeing . com

On there , somewhere, is the "Boeing Bump" a grph showing the runway uneveness against a/c performance.

Worth showing to the CP or CE

Sir George Cayley

[Desk Jockey]

There are maintenance requirements before and after visiting anything classed as a "rough runway" for B757/767 at least. (MLG pivot pin lube and later in life a truck strip) Depending on the build of your gear.
Required by service bulletin.

[Loose rivets]

I was PNF on an aircraft leaving a field in Yugoslavia nearly 40 years ago. The hammering on the undercarriage was so severe that in my opinion it degraded the performance.

This was born out by my call of V1 somewhere over the oggin.


The fleet manager was flying, and not a word was said, either at the time or later.

[OverRun]

Vaneev

There is a limit to roughness, although as Rainboe said, runways (should be) checked for performance and roughness and if the runway is operational you may assume it is considered acceptable. However ICAO guidance is very weak on the issue and the reality is that some runways can be rough (or can have 1 or 2 big bumps in them that really jolt the aircraft). Some ex-military concrete runways (especially in the Third World) can be real bone-shakers.

NASA found that the response of aircraft to runways required tentative limits on the vertical acceleration at the cockpit location. In practice, a runway could be judged as rough by some pilots and satisfactory by others. It was therefore necessary to relate roughness to cockpit acceleration, and concentrate repair efforts on those sections of the runway producing undesirable acceleration responses. Based on the NASA investigations, an acceptable maximum incremental cockpit acceleration from a pilot’s viewpoint was established at +/- 0.4 g. This was considered to be the dividing line between satisfactory and unsatisfactory runways, and any greater acceleration could cause loss of precise control of the aircraft and subsequent pilot difficulties.

It was then observed at Anchorage International Airport that a runway which had been satisfactory for piston aircraft could cause undesirable cockpit accelerations in jet transports. Furthermore, not all aircraft are affected similarly by a given roughness pattern. That is, for a given velocity over a given runway roughness pattern, aircraft of different sizes will respond in different ways. This response is dependent on the natural frequency of the aircraft rigid body (and its size) and the elastic response, such that resonant patterns can be created between the aircraft and the runway unevenness pattern. Some good work was then done by Spangler and Gerardi (who I seem to remember was an ex-Lockheed landing gear designer) and they developed software to measure the runway profile and then calculate the dynamic response in the cockpit for the various aircraft during takeoff or taxi. It is complex stuff.

Boeing got involved in runway roughness, initiated by a request in 1968 by Ethiopian Airlines to comment on the condition of the runway at Addis Ababa, which was a representative example of a runway subjectively felt to be too rough by experienced pilots. According to the pilot reports, in a typical operation certain isolated bumps on the runway felt extremely hard during takeoff and landing, and the airplane resounded with sharp jolts that seemed much more severe than a hard landing. It was determined that the severity of the jolt varied with speed and the wavelength of the bump, leading Boeing investigators to believe that an objective criteria should be developed based on single bump height and spacing limits.

To cut a long story short, they came up with the Boeing bump criteria. This is based on a considerable amount of testing and analysis, and is a lot more sophisticated than it looks. It is easy to use, and needs only a local surveyor to take simple measurements. The FAA like it, and are giving serious consideration to adopting it as their new standard. Given that ICAO guidance is weak in this specific area, I reckon Boeing have done a great job here, and I have found it to work well in practice.

Here is the bump criteria that Sir George referred to:
http://www.geocities.com/profemery/boeingbump.jpg

[werbil]

The roughness of the 'runways' that I operate from varies with the wind strength, wind direction, tide, currents and boats operating in the vicinity - I am a float plane pilot.

C208's on floats can experience the Concord STC - a drooped nose as a result of the firewall bending from operation in rough water. The maximum demonstrated wave height is 0.6m - not many runways have bumps that high on them. I understand that Cessna has a number of levels of firewall reinforcement to repair / help prevent this problem.

We use a number of techniques to minimize loads on the structure, most importantly looking for the smoothest water, paralleling swells, minimizing high speed operation on the water, use of reverse to stop quickly and flap techniques to get off the water. Some days it just gets too rough to operate - I've heard of pilots jarring their backs in rough water sometimes damaging aircraft and sometimes not.

[kenparry]

OverRun:

Fascinating stuff - that's the first time I have seen any proper analysis of rough runway effects.

A couple of stories:

When the RAF started operating Harriers from field sites, roughness became an issue. A practical test was evolved - if a LandRover could be driven down the strip at 40 mph without excessive discomfort to the driver (hardly an objective test) then it was OK for flying. It seemed to work, though.

The other: a Mediterranean airfield that had better remain anonymous in case the lawyers read this, 1990s. The airline I flew for at the time took B757 & 767 there, and the only runway had a severe bump from subsidence, so bad that a colleague's B767 on take-off was tossed into the air below V1 one day. We got Boeing to do an analysis of the QAR data, and they were seriously concerned about structural loads. After much argument, the runway was improved.

[OverRun]

Kenparry:

Actually driving down the strip in a Landrover is a jolly good method. It’s an old standby test much beloved of airport engineers. I can even quote it from the Australian manual of standards CASR part 139:
Note: An empirical test for runway riding quality is to drive a stiffly sprung vehicle such as a medium size utility or unladen truck along the runway at not less than 65 kph. If the ride is uncomfortable, then the surface needs to be graded and levelled.

If you have doubts about a runway (and also the runway strip) then ask to be driven along it. If I have doubts, I insist on using the airport manager’s own car. It is amazing how quickly the airport manager remembers that the strip is too rough when he is asked to risk his own property.

You’ve triggered a good thought though – Vaneev opened the discussion with a concern about a specific runway. I don’t much about the QAR and its accuracy of measurement (and I don’t know where the accelerometer is located and if it gives the same vertical acceleration as the pilots experience in the cockpit), but is it possible to access the data and see the instantaneous vertical acceleration along the runway?

If it goes over 0.4g, the runway is too rough and the airline has quantitative reason to complain to the airport (and to the country’s regulator).

Incidentally, Boeing found that most of the time that a rough runway was fixed was after pilot complaints and not through airport initiative. If anyone does follow this through, please post your findings here ( . . . . Vaneev :)).

[kenparry]

OverRun:

The QAR on the aircraft I'm referring to was not accessible in real time, only by post-flight data dump. As to accelerometer position, I don't know.

We did have some early B767-200 on which you could display a selection of parameters in real time on a small LED screen near the back of the centre stand, and load factor was one of those available. I don't recall ever looking at it while on the runway, as there were more important things to do.

Your comment about using the airport manager's car is telling............

[Flapping_Madly]

I am only SLF but if I may comment please.

Roughest runway I can recall is Hong Kong . A number of people in my party commented. I was surprised--it is a super new airport I think.