SOUTHAMPTON

[osbo]

LSM

“Sorry Osbo, my understanding is not flawed! Maybe my figures are a bit out of date following the advent of the iPad perf, granted. Still only available to those who have completed the LMS training and I admit it sounds a bit better.”

Sorry, your understanding of 175 performance is flawed because it’s based on data that is totally out of date and doesn’t maximise the aircraft’s capabilities using all of the available means. The new performance data is more than “a bit better” – it’s a lot better. For a start, in the example for 20 at SOU we can now make use of the improved performance offered by restricting the MACTOW to more than 16% - that gives an improvement of more than 500kg in itself. From your previous post I gather you didn’t take account of ECS OFF in your calc – that accounts for another 500kg. Also, each T/O calculation benefits from being a precise calculation rather than using worst case data produced to cover a huge range of variables on one sheet of paper.

“Even with a Dash load it'll only carry 5.5 tonnes of fuel, same as the Dash and even if you can lift that from SOU you're not getting as far as the Dash full stop. Increasing the RTOM will increase, even further, the operating costs of a 175 as opposed to the Dash.”

Just a minute! Using your planning data of 90kg/pax, even without performance restriction the max fuel the fully-loaded Dash can carry is:

MTOM 28998kg – TYPICAL ZFM 25220kg = 3778kg!!, considerably less than the 5.5 tonnes you quote!

As demonstrated in the previous post, using the same average pax weights, the 175 can lift a full load of 88 pax with 4500kg of fuel right up to 28C. The Dash starts to suffer from performance reduction when the temperature rises above 5C (15C on rwy 02), so that by the time the temperature reaches 28C it can only carry 2630kg of fuel (3100kg on rwy 02).

Let’s say that those two maximum fuel loads equate to roughly the fuel required (FOB) for the same sector on each aircraft, though the difference in fuel burn will be smaller.

Then to summarise,

1. with a full pax load where neither aircraft is performance limited, they have broadly similar range, but the 175 is carrying 10 more pax.

2. at SOU, where performance is an issue for the Dash, the 175 maintains its payload/range capability whilst the range of the Dash with max payload reduces significantly as the temperature rises. An EFB performance app for the Dash may improve this in the future, but point 1. above will still apply.

3. At airfields with longer runways the Dash and 175 offer similar range but with the 175 able to carry 10 more pax.

4. There is potential to increase the fuel load of the 175 by up to 2500kg (>2hrs flight time) by an increase to MTOM should it be required in future but that would incur higher nav charges for any aircraft so upgraded. This would considerably extend its range capability from longer runways, but it is not relevant to the discussion here.

As for operating costs, suffice to say that Flybe got a VERY good deal on the 175 and we are told that operating costs of the 175 vs Dash are really not a significant issue. Factor in the expected reliability benefits and much-improved customer experience and I think it will prove to be a big success as a Dash replacement on all but the shorter domestic routes.

It certainly does not suffer from performance problems at SOU, which is where all of this began with the incorrect statement that “trouble is the 175 performance from SOU is sadly lacking, to be kind about it. It's going to struggle to get as far as the Dash with a similar load!”

It's simply not so!