Engine Run Ups
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Engine Run Ups
The engineer who signed off on the construction of the ramp at Pakistan's Sialkot International Airport likely has some explaining to do after a Shaheen Air International Boeing 737-400 rearranged it some during a routine engine test. Engineers did a high power run-up of the No. 1 engine on June 19 and turned the parking area into a maelstrom of FOD. It appears the hard surface was made from the interlocking concrete paving stones that are commonly used for patios and garden walkways. They are set in a sand bed and interlock with each other, which is more than adequate for foot traffic and the occasional bicycle but not really up to 20,000 pounds of high bypass turbofan thrust from a CFM56 engine.
The jet blast threw the concrete missiles, each weighing a few pounds and with lots of pointy facets, into the fuselage and tail surfaces. A few dozen ended up on the horizontal stabilizer. It's not clear how much it will cost to fix the damage or whether the aircraft can even be repaired.
The jet blast threw the concrete missiles, each weighing a few pounds and with lots of pointy facets, into the fuselage and tail surfaces. A few dozen ended up on the horizontal stabilizer. It's not clear how much it will cost to fix the damage or whether the aircraft can even be repaired.
Some years ago a similar event occurred at Luton airport in the UK.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
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Sand is Not Enough
Thank you. Most of of us have seen this for a week or so and yes, it is still more than a bit silly! Sand-based foundations seem to work just fine for low-speed urban transits, both cars and light trains (light rail?). My guess is that it would also work -semi-well- as a slow speed taxi surface. Humph! when the back jets get anywhere beyond coasting idle, as in ANY increased thrust, yup... both sand and the pavers will move. And Yup again, if the thrust is significant, well - see the darn pix! While the ground operating crew should have known better... what goofy engineer built that pad in the first place. Sand and fine soil 'pavers' have supported a lot of Europe for a century or more; it is a well proven method. Please... It is NOT suitable for airport aprons or taxiways. Period.
In some nations, in days past, the lead engineer for a project like this may have been shot. I think we're all smarter these days and perhaps the fellow might enjoy some refresher training. The engineering error may be expensive, but I don't think that anyone will be shot as a result.
Errors happen, even in the professional engineering fields. Let this be a lesson to us all, regardless of our profession (or our secondary profession.) With wide enough distribution (and a few <chuckles>), perhaps this won't have to happen again.
and (bumping head against the wall) I guess three is enough...
In some nations, in days past, the lead engineer for a project like this may have been shot. I think we're all smarter these days and perhaps the fellow might enjoy some refresher training. The engineering error may be expensive, but I don't think that anyone will be shot as a result.
Errors happen, even in the professional engineering fields. Let this be a lesson to us all, regardless of our profession (or our secondary profession.) With wide enough distribution (and a few <chuckles>), perhaps this won't have to happen again.
and (bumping head against the wall) I guess three is enough...
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I think it's not that simple. Boeing and Airbus AMMs clearly state that engine runs must be performed on a stable surface. Forget about interlocking bricks. High power runs can't even be done on asphalt. It needs to be concrete.
The aircraft engineer performing the engine runs is also accountable.
The aircraft engineer performing the engine runs is also accountable.
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Some years ago a similar event occurred at Luton airport in the UK.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
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Those are amazing photos, which are also doing the rounds of airport engineers at the moment. They will no doubt find themselves into various technical presentations in the future.
Once again PPRUNE has taught me something, about pavers and jet blast. But first let me give some background to the use of concrete block pavers on airports.
There is a lot of block paving out there, used at many UK airports, Hong Kong, Cairns, Perth (Australia), Trondheim, Ben Gurion, etc. To illustrate their use, this is a quote from the literature:
“[have been used on] aircraft parking stands at Christchurch International Airport (International Stand 27 and Stand 34/35). The blocks have been laid on a 20mm thick layer of bedding sand on a cement stabilised basecourse layer with the blocks being sealed. To date the pavements are performing well under loading from Code E derivative aircraft.”
The use of concrete block pavers on airports is codified in several official standards or manuals, such as FAA ITEM P-502 Interlocking Concrete Pavement Construction For Airport Pavement. There is a very good manual on “Airfield Pavement Design With Concrete Pavers” written by Roy McQueen, John Knapton, John Emery (not me), and David Smith - Interlocking Concrete Pavement Institute – Updated May 2012. These authors are highly respected internationally.
However, there are certain situations where pavers are not recommended.
The British Ministry of Defense, British Aerospace, PLC, and the U.S. Air Force conducted tests on pavers exposed to high velocity jet exhaust. Although, the results of these experiments were favourable, concrete pavers are not recommended in airport locations subject to full power or reverse thrust, such as runways or apron areas where aircraft "power-back" operations are conducted. The FAA standard also says “The use of concrete pavers is not recommended for areas subjected to full power or reverse thrust (e.g. runways or apron areas where aircraft "power-back" operations are conducted).”
That pretty well suggests what happened at Pakistan's Sialkot International Airport. I do not know the technical details of the pavement, but I can see from the photos that the blocks are interlocking (as they should be) and they look to be the correct 80mm (3.125 ins) thick. There is bedding sand present, but possibly thicker than the required ¾ inch to 1 inch (20 mm to 25 mm); I cannot tell if the bedding sand meets the high quality standard needed. There is also the use of a geotextile under the sand which is recommended for certain bases (such as cement stabilised).
But the jointing sand looks a little odd, and even slightly missing in sections of undisturbed apron. The jointing sand is necessary to provide interlocking among the individual paver units. Aircraft loads are transmitted to surrounding pavers by shear forces through the joint sand, enabling the pavers and bedding sand to function as a distinct structural layer to allow distribution of loads in a manner similar to a hot mix asphalt layer. The sand should have been sealed (using something like an elastomeric urethane) to prevent its loss from jet blast. The joints are difficult to see in the photos but I am not certain that the jointing sand is always present, effective and sealed.
Based on past performance at airports, properly constructed concrete block pavers would be considered for:
- static parking positions with "tug-in/tug-out" or low engine speed "power-in/power-out" operations (excluding reverse engine thrust).
- low speed taxiways and taxi lanes (my own rule of thumb is an upper speed limit of 40 kph on concrete block pavers).
and this accident at Sialkot International Airport shows no reason to change that. It looks to me like the pavement was being used "outside the design envelope".
Once again PPRUNE has taught me something, about pavers and jet blast. But first let me give some background to the use of concrete block pavers on airports.
There is a lot of block paving out there, used at many UK airports, Hong Kong, Cairns, Perth (Australia), Trondheim, Ben Gurion, etc. To illustrate their use, this is a quote from the literature:
“[have been used on] aircraft parking stands at Christchurch International Airport (International Stand 27 and Stand 34/35). The blocks have been laid on a 20mm thick layer of bedding sand on a cement stabilised basecourse layer with the blocks being sealed. To date the pavements are performing well under loading from Code E derivative aircraft.”
The use of concrete block pavers on airports is codified in several official standards or manuals, such as FAA ITEM P-502 Interlocking Concrete Pavement Construction For Airport Pavement. There is a very good manual on “Airfield Pavement Design With Concrete Pavers” written by Roy McQueen, John Knapton, John Emery (not me), and David Smith - Interlocking Concrete Pavement Institute – Updated May 2012. These authors are highly respected internationally.
However, there are certain situations where pavers are not recommended.
The British Ministry of Defense, British Aerospace, PLC, and the U.S. Air Force conducted tests on pavers exposed to high velocity jet exhaust. Although, the results of these experiments were favourable, concrete pavers are not recommended in airport locations subject to full power or reverse thrust, such as runways or apron areas where aircraft "power-back" operations are conducted. The FAA standard also says “The use of concrete pavers is not recommended for areas subjected to full power or reverse thrust (e.g. runways or apron areas where aircraft "power-back" operations are conducted).”
That pretty well suggests what happened at Pakistan's Sialkot International Airport. I do not know the technical details of the pavement, but I can see from the photos that the blocks are interlocking (as they should be) and they look to be the correct 80mm (3.125 ins) thick. There is bedding sand present, but possibly thicker than the required ¾ inch to 1 inch (20 mm to 25 mm); I cannot tell if the bedding sand meets the high quality standard needed. There is also the use of a geotextile under the sand which is recommended for certain bases (such as cement stabilised).
But the jointing sand looks a little odd, and even slightly missing in sections of undisturbed apron. The jointing sand is necessary to provide interlocking among the individual paver units. Aircraft loads are transmitted to surrounding pavers by shear forces through the joint sand, enabling the pavers and bedding sand to function as a distinct structural layer to allow distribution of loads in a manner similar to a hot mix asphalt layer. The sand should have been sealed (using something like an elastomeric urethane) to prevent its loss from jet blast. The joints are difficult to see in the photos but I am not certain that the jointing sand is always present, effective and sealed.
Based on past performance at airports, properly constructed concrete block pavers would be considered for:
- static parking positions with "tug-in/tug-out" or low engine speed "power-in/power-out" operations (excluding reverse engine thrust).
- low speed taxiways and taxi lanes (my own rule of thumb is an upper speed limit of 40 kph on concrete block pavers).
and this accident at Sialkot International Airport shows no reason to change that. It looks to me like the pavement was being used "outside the design envelope".
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Yes, was just about to say that I've seen these used on the cargo ramps at Cairns. (Maybe elsewhere on the airport too, I've only been on the cargo ramps )
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I would never have guessed that a shed (Shorts 330) could have chewed up a block-paved runway turning area. It’s a small aircraft: 30 pax, 2 x 1198hp turboprops, MTOW 10.4 tonnes, and tyre pressure about 550 kPa (80 psi). I guess I’m always learning something.
The choice for concrete block pavers is assuredly engineer driven and they are not chosen by accountants. After all, there are 3 whole words and 19 letters in the phrase ‘concrete block pavers' and most accountants would need a whole financial year to count that high.
Cost-wise, concrete block pavers are probably not cheaper than asphalt, but are cheaper than concrete. Their attraction is that they give a surfacing with the toughness of concrete, but are much quicker to install than concrete and are easy to reconfigure and repair
I particularly like them where the aircraft loads are light but the tyre pressures are very high or there are helicopter skids. Aprons for fighter planes or biz jets. On helicopter aprons, skids don’t damage pavers as they spread outwards under the weight of the helicopter; but skids easily tear asphalt and chip seals (especially in hot climates). Concrete block pavers are popular with others on larger aircraft aprons because they are tough enough to take all the trollies and other ground furniture, they resist the tearing up by fuel trucks and fire engines (which can do more damage than an aircraft as they rip around under full throttle and at high weight), pavers don’t worry when things get dropped on them, and fuel and hydraulic spills don’t damage them. And if there is some damage (and I am thinking of the typical damage of about a square metre or so and not the much larger damage at Pakistan Sialkot International Airport) then they are quickly and easily replaced. Actually the damage to the apron at Sialkot International Airport will also be easy and cheap to fix but not the damage to the Boeing. Pavers are quick and lay and to pick up, which means that the apron can be re-configured easily as the terminal grows and reconfigures.
High power engine runs are usually done in restricted and specific areas. The jet blast (and noise) are prime considerations for the restrictions. Looking at the photos at the start of this thread, the Boeing was in front of the ATC tower, and on a regular parking bay. It was not a specific engine run-up area. The bay was the end one – in the centre of the Google Earth picture of the airport shown below.
The terminal and ATC tower are at the top of the picture (not a very good one I’m afraid), and the aircraft was parked aiming at them, towards the top of the picture. There is nothing behind the aircraft except the runway so an engine run would have been possible. There are no workshops, hangars, engine maintenance companies anywhere near the aircraft, so engine run-ups would not have been anticipated. And there is nothing to suggest to the casual observer that a high power run would ever be done on that parking bay.
Umm, I would have thought that the apron stand where the aircraft was parked was a good candidate for concrete block pavers. And the FAA and CAA rules would agree.
Still, I reckon there is scope for a suitable note where the State has an aerodrome manual such as MOS 139 (Australia). I just looked at the UK CAP 168, and they have it already and said very nicely too:
12.7 The use of block pavers on aerodrome movement areas
12.7.1 It is recommended that pavers should normally only be used to surface the following categories of aircraft pavements:
a) Aircraft stands.
b) Low speed taxiways not subject to significant jet blast or propeller wash.
c) Aircraft maintenance areas not subject to significant jet blast or propeller wash.
d) Helicopter pads.
12.7.2 Block pavers should normally not be used to surface the following categories of aircraft pavements:
a) Runways.
b) Areas where aircraft engines are run at high thrust values.
c) High speed taxiways.
The choice for concrete block pavers is assuredly engineer driven and they are not chosen by accountants. After all, there are 3 whole words and 19 letters in the phrase ‘concrete block pavers' and most accountants would need a whole financial year to count that high.
Cost-wise, concrete block pavers are probably not cheaper than asphalt, but are cheaper than concrete. Their attraction is that they give a surfacing with the toughness of concrete, but are much quicker to install than concrete and are easy to reconfigure and repair
I particularly like them where the aircraft loads are light but the tyre pressures are very high or there are helicopter skids. Aprons for fighter planes or biz jets. On helicopter aprons, skids don’t damage pavers as they spread outwards under the weight of the helicopter; but skids easily tear asphalt and chip seals (especially in hot climates). Concrete block pavers are popular with others on larger aircraft aprons because they are tough enough to take all the trollies and other ground furniture, they resist the tearing up by fuel trucks and fire engines (which can do more damage than an aircraft as they rip around under full throttle and at high weight), pavers don’t worry when things get dropped on them, and fuel and hydraulic spills don’t damage them. And if there is some damage (and I am thinking of the typical damage of about a square metre or so and not the much larger damage at Pakistan Sialkot International Airport) then they are quickly and easily replaced. Actually the damage to the apron at Sialkot International Airport will also be easy and cheap to fix but not the damage to the Boeing. Pavers are quick and lay and to pick up, which means that the apron can be re-configured easily as the terminal grows and reconfigures.
High power engine runs are usually done in restricted and specific areas. The jet blast (and noise) are prime considerations for the restrictions. Looking at the photos at the start of this thread, the Boeing was in front of the ATC tower, and on a regular parking bay. It was not a specific engine run-up area. The bay was the end one – in the centre of the Google Earth picture of the airport shown below.
The terminal and ATC tower are at the top of the picture (not a very good one I’m afraid), and the aircraft was parked aiming at them, towards the top of the picture. There is nothing behind the aircraft except the runway so an engine run would have been possible. There are no workshops, hangars, engine maintenance companies anywhere near the aircraft, so engine run-ups would not have been anticipated. And there is nothing to suggest to the casual observer that a high power run would ever be done on that parking bay.
Umm, I would have thought that the apron stand where the aircraft was parked was a good candidate for concrete block pavers. And the FAA and CAA rules would agree.
Still, I reckon there is scope for a suitable note where the State has an aerodrome manual such as MOS 139 (Australia). I just looked at the UK CAP 168, and they have it already and said very nicely too:
12.7 The use of block pavers on aerodrome movement areas
12.7.1 It is recommended that pavers should normally only be used to surface the following categories of aircraft pavements:
a) Aircraft stands.
b) Low speed taxiways not subject to significant jet blast or propeller wash.
c) Aircraft maintenance areas not subject to significant jet blast or propeller wash.
d) Helicopter pads.
12.7.2 Block pavers should normally not be used to surface the following categories of aircraft pavements:
a) Runways.
b) Areas where aircraft engines are run at high thrust values.
c) High speed taxiways.
Quote:
Originally Posted by eckhard View Post
Some years ago a similar event occurred at Luton airport in the UK.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
Just curious to know if Luton still has this area or if anyone knows of any other major airports with areas like this?
Originally Posted by eckhard View Post
Some years ago a similar event occurred at Luton airport in the UK.
The turning pad at the start of the runway was paved with these kind of blocks. A departing airliner applied take-off thrust while on the pad and blew away several paving blocks. Damage to horizontal stabiliser was discovered after the subsequent landing at destination, after a normal flight.
Just curious to know if Luton still has this area or if anyone knows of any other major airports with areas like this?
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A couple more incidents for us to think about...
Accident: Lufthansa B733 at Katowice on May 2nd 2015, engines disloged runway pavement, debris struck horizontal stabilizer, aircraft flew to destination
Accident: Brussels B733 at Mbuji-Mayi on Aug 19th 2015, stabilizer damaged by dislodged runway pavement
Accident: Lufthansa B733 at Katowice on May 2nd 2015, engines disloged runway pavement, debris struck horizontal stabilizer, aircraft flew to destination
Accident: Brussels B733 at Mbuji-Mayi on Aug 19th 2015, stabilizer damaged by dislodged runway pavement
