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Why is 0ft a valid target altitude for an autopilot?
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up vote
6
down vote
favorite
Inspired by this story;
The pilot of a Flybe plane that dropped 500ft (152m) in 18 seconds had
selected the wrong autopilot setting shortly after take-off, an
inquiry has found...
...The plane climbed to 1,500ft, but then pitched and "descended
rapidly" because the autopilot was set with a target altitude of 0ft.
Why is 0ft a valid target value for the autopilot? Is there any practical use for being able to set it so low and are there safety features that would prevent the plane just hitting the deck?
autopilot altitude
asked 6 hours ago
Darren
1312
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show 6 more comments
up vote
6
down vote
favorite
Inspired by this story;
The pilot of a Flybe plane that dropped 500ft (152m) in 18 seconds had
selected the wrong autopilot setting shortly after take-off, an
inquiry has found...
...The plane climbed to 1,500ft, but then pitched and "descended
rapidly" because the autopilot was set with a target altitude of 0ft.
Why is 0ft a valid target value for the autopilot? Is there any practical use for being able to set it so low and are there safety features that would prevent the plane just hitting the deck?
autopilot altitude
asked 6 hours ago
Darren
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
2
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
1
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
1
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
1
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago
 |Â
show 6 more comments
up vote
6
down vote
favorite
up vote
6
down vote
favorite
Inspired by this story;
The pilot of a Flybe plane that dropped 500ft (152m) in 18 seconds had
selected the wrong autopilot setting shortly after take-off, an
inquiry has found...
...The plane climbed to 1,500ft, but then pitched and "descended
rapidly" because the autopilot was set with a target altitude of 0ft.
Why is 0ft a valid target value for the autopilot? Is there any practical use for being able to set it so low and are there safety features that would prevent the plane just hitting the deck?
autopilot altitude
asked 6 hours ago
Darren
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Inspired by this story;
The pilot of a Flybe plane that dropped 500ft (152m) in 18 seconds had
selected the wrong autopilot setting shortly after take-off, an
inquiry has found...
...The plane climbed to 1,500ft, but then pitched and "descended
rapidly" because the autopilot was set with a target altitude of 0ft.
Why is 0ft a valid target value for the autopilot? Is there any practical use for being able to set it so low and are there safety features that would prevent the plane just hitting the deck?
autopilot altitude
autopilot altitude
asked 6 hours ago
Darren
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Darren
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Darren
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
Darren
1312
asked 6 hours ago
Darren
1312
1312
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Darren is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
2
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
1
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
1
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
1
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago
 |Â
show 6 more comments
2
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
1
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
1
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
1
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago
2
2
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
1
1
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
1
1
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
1
1
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago
 |Â
show 6 more comments
3 Answers
3
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up vote
3
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The answer is no you would never depart with the altitude preselect at 0. You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. All would be at least a 1000 ft above the airport at minimum.
You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate.
With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. However...
The -8 400 has coupled VNAV, which adds an extra wrinkle. With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS.
So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued.
answered 4 hours ago
John K
10.6k1131
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
add a comment |Â
up vote
2
down vote
Quite simply, it's because sometimes you fly below sea level. There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level.
There are numerous areas in the world that are below sea level. For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! It's added as an additional option to cover a small set of scenarios. A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude).
answered 4 hours ago
Matt
1,243419
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
add a comment |Â
up vote
0
down vote
Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. (see also What is wrong about this interpretation of QFE and QNH?)
QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold.
So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
answered 10 mins ago
user71659
2,114617
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
The answer is no you would never depart with the altitude preselect at 0. You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. All would be at least a 1000 ft above the airport at minimum.
You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate.
With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. However...
The -8 400 has coupled VNAV, which adds an extra wrinkle. With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS.
So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued.
answered 4 hours ago
John K
10.6k1131
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
add a comment |Â
up vote
3
down vote
The answer is no you would never depart with the altitude preselect at 0. You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. All would be at least a 1000 ft above the airport at minimum.
You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate.
With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. However...
The -8 400 has coupled VNAV, which adds an extra wrinkle. With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS.
So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued.
answered 4 hours ago
John K
10.6k1131
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
add a comment |Â
up vote
3
down vote
up vote
3
down vote
The answer is no you would never depart with the altitude preselect at 0. You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. All would be at least a 1000 ft above the airport at minimum.
You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate.
With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. However...
The -8 400 has coupled VNAV, which adds an extra wrinkle. With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS.
So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued.
answered 4 hours ago
John K
10.6k1131
The answer is no you would never depart with the altitude preselect at 0. You would normally set the initial level off altitude provided in your departure clearance, or an initial level off altitude indicated in the SID, or you might set a level off altitude that you have decided to use as a level off for the single engine profile in the event of engine failure, based on the terrain around the airport. All would be at least a 1000 ft above the airport at minimum.
You dial up that altitude in the AP's altitude preselect window, usually during the configuration setup during or after the crew departure briefing. When you are airborne, you will normally select the autopilot's speed hold mode (on the -8 AP it's called IAS mode) which makes the flight director command a pitch attitude to hold bug speed, then when you pass 400 feet or above, you engage A/P in IAS mode and it will pitch the plane to hold the bug speed you select during the departure. In IAS mode, whether you climb or descend depends on the power setting, so when you are climbing and descending in IAS mode you regulate the climb/descent with power while the AP pitches to hold the speed. You can also use VS mode, or vertical speed mode, and the AP will now pitch to a preset vertical climb or descent rate.
With those two vertical modes, the incident description doesn't make a lot of sense as they would have had to have selected VS mode and dialed in a descent rate, or been in IAS mode and cut the power. However...
The -8 400 has coupled VNAV, which adds an extra wrinkle. With VNAV engaged, the autopilot will pitch to climb or descend to an altitude preselect independently of IAS or VS mode, instead of just hold an airspeed or vertical speed, until a preselect altitude is captured. Coupled VNAV can also follow step climbs in a SID or step descents in a STAR if that is programmed into the FMS.
So my guess here is that they forgot to set the altitude preselect for their planned departure level off altitude, then engaged the autopilot in VNAV mode during the climbout, which caused the plane to dive to the existing altitude preselect of 0 feet, upon which hilarity ensued.
answered 4 hours ago
John K
10.6k1131
edited 11 mins ago
answered 4 hours ago
John K
10.6k1131
answered 4 hours ago
John K
10.6k1131
answered 4 hours ago
John K
10.6k1131
10.6k1131
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
add a comment |Â
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
1
1
For certain values of "hilarity."
– Zach Lipton
1 hour ago
For certain values of "hilarity."
– Zach Lipton
1 hour ago
Nice answer. Thanks.
– Darren
28 mins ago
Nice answer. Thanks.
– Darren
28 mins ago
add a comment |Â
up vote
2
down vote
Quite simply, it's because sometimes you fly below sea level. There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level.
There are numerous areas in the world that are below sea level. For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! It's added as an additional option to cover a small set of scenarios. A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude).
answered 4 hours ago
Matt
1,243419
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
add a comment |Â
up vote
2
down vote
Quite simply, it's because sometimes you fly below sea level. There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level.
There are numerous areas in the world that are below sea level. For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! It's added as an additional option to cover a small set of scenarios. A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude).
answered 4 hours ago
Matt
1,243419
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
add a comment |Â
up vote
2
down vote
up vote
2
down vote
Quite simply, it's because sometimes you fly below sea level. There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level.
There are numerous areas in the world that are below sea level. For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! It's added as an additional option to cover a small set of scenarios. A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude).
answered 4 hours ago
Matt
1,243419
Quite simply, it's because sometimes you fly below sea level. There's a couple stories out there of aircraft navigation systems acting a bit odd due to their flight below sea level. For example, there is this one, which involves a C-130 landing on an airfield that is 1,210 feet below sea level.
There are numerous areas in the world that are below sea level. For example, flying at sealevel above Laguna Salada, Mexico means you are still 30 feet above the ground! It's added as an additional option to cover a small set of scenarios. A pilot is certainly not expected to select the incorrect altitude setting, as this is something that you should always doublecheck. Beyond that, he should not have enabled his autopilot so soon after takeoff (unless 1,500 was his cruising altitude).
answered 4 hours ago
Matt
1,243419
answered 4 hours ago
Matt
1,243419
answered 4 hours ago
Matt
1,243419
answered 4 hours ago
Matt
1,243419
1,243419
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
add a comment |Â
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
"For example, there is this one" - did you forget a link? I'd like to click it!
– Steve
3 hours ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
It's more than acceptable to engage your autopilot at 1,500 feet in most planes. Most of the ones that I fly specify 1,000 feet as the minimum, and in busy airspace or when you want to devote more attention to avoiding weather, it can even be a good idea.
– Lnafziger
17 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
You can use the autopilot as soon as 400 ft AGL on the 737NG, and on the A320, its 100 ft AGL! (On the A320 though, you have to be already using the flight director/SRS, so you know it's going do something sensible)
– user71659
3 mins ago
add a comment |Â
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Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. (see also What is wrong about this interpretation of QFE and QNH?)
QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold.
So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
answered 10 mins ago
user71659
2,114617
add a comment |Â
up vote
0
down vote
Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. (see also What is wrong about this interpretation of QFE and QNH?)
QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold.
So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
answered 10 mins ago
user71659
2,114617
add a comment |Â
up vote
0
down vote
up vote
0
down vote
Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. (see also What is wrong about this interpretation of QFE and QNH?)
QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold.
So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
answered 10 mins ago
user71659
2,114617
Besides flying below sea level, a situation for low and negative altimeter readings is use of QFE altimetry. (see also What is wrong about this interpretation of QFE and QNH?)
QFE altimetry which was used by some airlines (gone by now), and is still in use in Russia (undergoing phase-out), is where you set the altimeter's reference pressure so that it reads zero at some ground reference point, typically the runway threshold.
So if the runway is above you, on terrain, you will fly at a negative height and your altimeters will show as such.
answered 10 mins ago
user71659
2,114617
answered 10 mins ago
user71659
2,114617
answered 10 mins ago
user71659
2,114617
answered 10 mins ago
user71659
2,114617
2,114617
add a comment |Â
add a comment |Â
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2
To cruise at low altitude in Death Valley?
– quiet flyer
6 hours ago
1
@quietflyer OK, good point that the ground level might be below 0ft sea level, I hadn’t thought of that. But in my head I imagined there would be some kind of buffer below where the autopilot couldn’t be trusted.
– Darren
6 hours ago
1
Yes. me too, that's why I didn't form it into a real answer. Good question.
– quiet flyer
6 hours ago
Which plane was that? Dash8? Bae146 or ATR? After it will depend of the autopilot coupled with the FD. For Airbus and Boeing the minimum is 100ft. But the autopilot is capable to land the aircraft so, it is able to go below 0ft ASL if you land in Amsterdam for example.
– Chris Lau
6 hours ago
1
@ChrisLau - during auto land in the Boeing, I believe that at GS capture the Go Around mode is armed and, depending on company procedures, the missed approach altitude is (pre)set in the altitude selector. (because the AP is locked on the approach and won't go to the altitude in the MCP altitude selected unless GA (toga) is pushed).
– 757toga
5 hours ago