Weight restrictions
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Weight restrictions
I have recently had the misfortune of trying to get on as a stand-by non-rev passenger on SJO-IAH. The aircraft, a 737-800, left with 7 seats empty while I did not get on. I was told by the gate agent that this has been the case very often out of SJO, and aircraft have left with as many as 17 empty seats within the past week while leaving passengers behind.
Can someone explain to me why would this happen on a regular basis, with the 738 having capability to fly a route about twice the distance of SJO-IAH under more favourable conditions? I thought with such a relatively light fuel load, you could easily fill the plane to capacity with pax, and did not even consider the possibility that there could be a weight restriction when making my travel plans. BTW, the same airline flies the same aircraft SJO-EWR, which is a five and a half hour flight compared to the 3 hour SJO-IAH. They have weight restrictions on SJO-EWR, which is not surprising to me.
I hope this is in the right forum - its my first post, although I've been lurking on this site for a few years and find it very informative.
Martin
Can someone explain to me why would this happen on a regular basis, with the 738 having capability to fly a route about twice the distance of SJO-IAH under more favourable conditions? I thought with such a relatively light fuel load, you could easily fill the plane to capacity with pax, and did not even consider the possibility that there could be a weight restriction when making my travel plans. BTW, the same airline flies the same aircraft SJO-EWR, which is a five and a half hour flight compared to the 3 hour SJO-IAH. They have weight restrictions on SJO-EWR, which is not surprising to me.
I hope this is in the right forum - its my first post, although I've been lurking on this site for a few years and find it very informative.
Martin
Too mean to buy a long personal title
Can someone explain to me why would this happen on a regular basis, with the 738 having capability to fly a route about twice the distance of SJO-IAH under more favourable conditions? I thought with such a relatively light fuel load, you could easily fill the plane to capacity with pax, and did not even consider the possibility that there could be a weight restriction when making my travel plans.
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Hi Martin - I'm gonna move this to the questions forum because it appears to require some specialist knowledge. Good luck and come back to Pax/SLF when you have an answer.
Without knowing anything about the specific aircraft or airport, some general reasons that you might be weight limited would be:
1. Runway length - short runway requires lower weight to allow the aircraft to take-off OR abort the take-off safely.
2. Obstacles surrounding the airfield - mountains, buildings, and towers may dictate a lower aircraft weight to allow it to climb sufficiently after having some kind of engine failure.
3. Hot day - heat reduces aircraft performance which affects it's ability to take-off and climb.
4. Airport at a high altitude - Like heat, the lower atmospheric pressure at high altitudes results in a loss in aircraft performance.
5. Fuel requirements - A long flight on one day may require less fuel than a short flight on another day as extra fuel is required if the weather at the destination is forecast to be dodgy.
Each of these factors may have a minimal impact on their own but sometimes you may be affected by several of them.
1. Runway length - short runway requires lower weight to allow the aircraft to take-off OR abort the take-off safely.
2. Obstacles surrounding the airfield - mountains, buildings, and towers may dictate a lower aircraft weight to allow it to climb sufficiently after having some kind of engine failure.
3. Hot day - heat reduces aircraft performance which affects it's ability to take-off and climb.
4. Airport at a high altitude - Like heat, the lower atmospheric pressure at high altitudes results in a loss in aircraft performance.
5. Fuel requirements - A long flight on one day may require less fuel than a short flight on another day as extra fuel is required if the weather at the destination is forecast to be dodgy.
Each of these factors may have a minimal impact on their own but sometimes you may be affected by several of them.
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Also got to think about max zero fuel weight.
I have flown a max'ed out zfw 747-400 from Perth to Singapore (4.5 hours) before with only a half load of passengers due to the cargo weight.
About 60 tonnes of payload I guess, of which only 20 tonnes down to pax. I believe something to do with the Australian coin minting coins for Singapore or some such....
Would have looked good for staff travel, 350+ capacity, 170+ free seats, sorry sir, it's weight limited!
I have flown a max'ed out zfw 747-400 from Perth to Singapore (4.5 hours) before with only a half load of passengers due to the cargo weight.
About 60 tonnes of payload I guess, of which only 20 tonnes down to pax. I believe something to do with the Australian coin minting coins for Singapore or some such....
Would have looked good for staff travel, 350+ capacity, 170+ free seats, sorry sir, it's weight limited!
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TopBunk - the max zero fuel weight limit seems like the most plausible cause to me, however I would not think there would be a lot of space available for cargo with 148 pax with check-in luggage returning from vacation in a 738. I did see some boxes packed with seafood being loaded onto another plane I did get on to, but it seems that the weight of the additional cargo taken on could not have been very much mostly due to cargo hold volume limitations.
Aerocat - most of your reasons like obstacles, runway length, runway altitude, etc., would not make day-to-day differences in weight restriction. The day to day temprerature variations at SJO are remarkably minimal as well. Could bad weather at IAH (high winds, heavy rain, which was the case that week) make that much of a difference? My thinking was that a 738 on a 1300nm flight is going out with fuel tanks almost half-empty, therefore pretty light, even if an extra hour worth of fuel is taken on...
I just found it remarkable that an SJO-EWR flight on the same day using the same equipment would go out with a similar weight restriction, and EWR is not only about 600nm further, but also known for its ATC caused delays.
Aerocat - most of your reasons like obstacles, runway length, runway altitude, etc., would not make day-to-day differences in weight restriction. The day to day temprerature variations at SJO are remarkably minimal as well. Could bad weather at IAH (high winds, heavy rain, which was the case that week) make that much of a difference? My thinking was that a 738 on a 1300nm flight is going out with fuel tanks almost half-empty, therefore pretty light, even if an extra hour worth of fuel is taken on...
I just found it remarkable that an SJO-EWR flight on the same day using the same equipment would go out with a similar weight restriction, and EWR is not only about 600nm further, but also known for its ATC caused delays.
