Ask The Pilot

[AviatorInsight]

For those familiar with Melbourne's 3AW radio station, on today's breakfast show they had this rumor regarding pilots managing fuel, etc..

What pilots are being told to do as fuel crisis worsens

On Tuesday’s edition of the Rumour File, Ross Stevenson revealed what pilots are being told to do during the current fuel crisis. The fuel crisis continues to have a huge impact on all industries, with aviation being one of them. “75% full won’t cut it,” Stevenson said on 3AW Breakfast. Press...

www.3aw.com.au

Not much detail in this audio clip, though, so difficult to know the full story.

Aviator Insight, can you shed any light on this?

That’s a great rumour.

We haven’t been told not to take off unless it’s full . If the loads are insufficient then ops will cancel the flight before I even get to the airport.

However, has anyone noticed a lot more idle reverse landings going on around the VA network? That’s one fuel saving initiative that has been brought in (albeit a couple of weeks prior to the conflict kicking off). Single engine taxi, and APU usage on the ground were all in effect months prior as well (not that I necessarily agree with any of these).

 

[NM]

That’s a great rumour.

We haven’t been told not to take off unless it’s full . If the loads are insufficient then ops will cancel the flight before I even get to the airport.

However, has anyone noticed a lot more idle reverse landings going on around the VA network? That’s one fuel saving initiative that has been brought in (albeit a couple of weeks prior to the conflict kicking off). Single engine taxi, and APU usage on the ground were all in effect months prior as well (not that I necessarily agree with any of these).

A company policy of using idle reverse did wonders for VH-OJH's golfing excursion in BKK back in 1999. Are there guard rails around when you should and should not use idle reverse, such not use idle reverse on a wet runway?

 

[AviatorInsight]

A company policy of using idle reverse did wonders for VH-OJH's golfing excursion in BKK back in 1999. Are there guard rails around when you should and should not use idle reverse, such not use idle reverse on a wet runway?

Yes there is, wet runway is one of them, but if you have a quick turnaround and you’ve landed near the max landing weight, then the brake cooling times will definitely come into play and you’ll need to consider if idle reverse is worth it.

 

[jb747]

A company policy of using idle reverse did wonders for VH-OJH's golfing excursion in BKK back in 1999. Are there guard rails around when you should and should not use idle reverse, such not use idle reverse on a wet runway?

There's nothing wrong with the use of idle reverse. The issue that QF had was that they were pushing its use as the standard, COMBINED with the use of flap 25. As options for when the weather is suitable they're fine. But pushing them so hard that some FOs had never landed the aircraft with F30 was simply stupid. They had quite a bit of push back from the line pilots, but management refused to listen. And we all know how that ended.

 

[Beano]

Do jet engines have gears, and if not why not?

 

[straitman]

Do jet engines have gears, and if not why not?

The answer to this is quite long winded and complicated. To that end the following is from Chat GPT:

They actually can have gears—but most turbine engines traditionally don’t. The reason comes down to how turbines produce power and what they’re best at.

1. Turbines love spinning fast​

Gas turbines (like jet engines or turboprops) operate most efficiently at very high RPM—often tens of thousands of revolutions per minute. That’s where they produce the best power-to-weight ratio.

But many things they drive—like propellers or fans—work best at much lower speeds.

So you’ve got a mismatch:

• Turbine: high speed
• Propeller/fan: lower speed

2. Why not just add gears?​

You can, but gears introduce problems:

• Weight – gearboxes are heavy (a big issue in aircraft)
• Complexity – more parts = more failure points
• Maintenance – gears need lubrication, inspection, and can wear out
• Losses – some energy is lost through friction

Because turbines are already very efficient and powerful, engineers often prefer to avoid adding a gearbox if possible.

3. How engines solve it without gears​

Instead of gearing down, many engines use:

• Large multi-stage turbines to extract energy more gradually
• Direct-drive designs where the fan/prop is matched to turbine speed
• Multiple shafts (spools) spinning at different speeds internally

4. But some turbine engines DO use gears​

Modern designs increasingly use gearboxes where it makes sense.

A good example is the geared turbofan:

• Geared Turbofan engines use a reduction gearbox so:
  • The turbine spins fast (efficient)
  • The fan spins slower (quieter and more efficient)

A well-known example:

• Pratt & Whitney PW1000G

5. When gears are common​

Gears are used more often in:

• Turboprop engines (to slow the propeller)
• Helicopter turbine engines
• Marine and industrial turbines

Bottom line​

Turbine engines don’t avoid gears entirely—they just avoid them unless the benefits outweigh the downsides. Historically, simplicity, weight, and reliability made gearless designs preferable—but modern engineering is bringing gears back where they improve efficiency.

 

[straitman]

An example of this is the Alison C30 that was/is used in many smaller helicopters:

The Allison 250-C30 (often just called the C30) is a turboshaft engine, and like most small gas turbines it runs at very high internal RPM.

Key speeds (approximate)​

• Gas generator (Ng): up to ~51,000 RPM
• Power turbine (Np): around 33,000 RPM internally
• Output shaft (after gearbox): typically about 6,000 RPM (or less, depending on installation)

What that means​

• The gas generator section (compressor + turbine) spins extremely fast—this is where the engine makes its power.
• The power turbine extracts that energy and drives the output.
• A reduction gearboxthen slows it way down to a usable speed for:
  • Helicopter rotors
  • Props (in turboprop conversions)
  • Other machinery

Real-world context​

In helicopters using this engine (like variants of the Bell 206 JetRanger), the main rotor typically turns at only about 300–400 RPM, so there’s massive gear reduction between the turbine and the rotor.

 

[Beano]

The answer to this is quite long winded and complicated. To that end the following is from Chat GPT.

They actually can have gears—but most turbine engines traditionally don’t. The reason comes down to how turbines produce power and what they’re best at.

1. Turbines love spinning fast​

Gas turbines (like jet engines or turboprops) operate most efficiently at very high RPM—often tens of thousands of revolutions per minute. That’s where they produce the best power-to-weight ratio.

But many things they drive—like propellers or fans—work best at much lower speeds.

So you’ve got a mismatch:

• Turbine: high speed
• Propeller/fan: lower speed

2. Why not just add gears?​

You can, but gears introduce problems:

• Weight – gearboxes are heavy (a big issue in aircraft)
• Complexity – more parts = more failure points
• Maintenance – gears need lubrication, inspection, and can wear out
• Losses – some energy is lost through friction

Because turbines are already very efficient and powerful, engineers often prefer to avoid adding a gearbox if possible.

3. How engines solve it without gears​

Instead of gearing down, many engines use:

• Large multi-stage turbines to extract energy more gradually
• Direct-drive designs where the fan/prop is matched to turbine speed
• Multiple shafts (spools) spinning at different speeds internally

4. But some turbine engines DO use gears​

Modern designs increasingly use gearboxes where it makes sense.

A good example is the geared turbofan:

• Geared Turbofan engines use a reduction gearbox so:
  • The turbine spins fast (efficient)
  • The fan spins slower (quieter and more efficient)

A well-known example:

• Pratt & Whitney PW1000G

5. When gears are common​

Gears are used more often in:

• Turboprop engines (to slow the propeller)
• Helicopter turbine engines
• Marine and industrial turbines

---

Bottom line​

Turbine engines don’t avoid gears entirely—they just avoid them unless the benefits outweigh the downsides. Historically, simplicity, weight, and reliability made gearless designs preferable—but modern engineering is bringing gears back where they improve efficiency.

Thanks. I knew turbo props could have gears. I was wondering why gas turbine engines can allow the aircraft to taxi at a range of slow speeds whilst providing enough power for take-off. Is this to do with the turn-down ratio?

 

[Saab34]

AV did you end up getting your Captain upgrade?

 

[AviatorInsight]

AV did you end up getting your Captain upgrade?

Haven’t been awarded it yet. I’m hoping they’ll do a base balance of pilot numbers next month and then see what is left over. Last time I checked I was still 57 slots away from holding Sydney and that was back in January.

Fingers are still crossed.

 

[Saab34]

Haven’t been awarded it yet. I’m hoping they’ll do a base balance of pilot numbers next month and then see what is left over. Last time I checked I was still 57 slots away from holding Sydney and that was back in January.

Fingers are still crossed.

Good to hear you are nearly there.

So a new FO joining today would be waiting a long time for an upgrade? Someone was telling me it’s 20 years for a Qantas 737 Captain upgrade.