Boeing 777 plane crash-lands at San Francisco airport

[manarak]

interesting experts' commentary:

http://edition.cnn.com/2013/07/07/us/california-plane-experts-cause/index.html

comment about the comment:

If the pilots missed the NOTAM, and the GS OFF flags on their FD/HSI, they could have been following a "null" signal into the ground short of the runway. By the time they noticed they were coming in short of the runway, and applied power, it was too late. Very similar incident happened going into Rio around 10-12 years ago on a BA 777, but they noticed the error earlier and corrected.

[Mosha]

Yes as far as hitting a wall is concerned at low speed (but not at near take-off speed) but even modern jets can float on water - at least for a while. Didn't a pilot land his 737 on the Hudson river a while back?

Nope but they did land an airbus A320.

[manarak]

landing trajectories of a safe landing and flight 214 compared:

https://twitter.com/sbaker/status/353611787750494208/photo/1

Wow... pretty interesting technology that allows the tracking and recording of such things... seems to be comparing the descent of the same flight the day before with the descent on the day of the crash. Drastically different.

July 5

PS0232.jpg

July 6

PS0233.jpg

If I put together the comparison of the flight trajectories and the fact that pilots requested emergency vehicles before the crash, the pilot error becomes a less likely scenario. Still likely, but less so. They might also have been let down by the engines.

[lomatopo]

and the fact that pilots requested emergency vehicles before the crash

Is there a source for this detail? I haven't read/heard a mention of this request. Did the flight deck made this request well out from the airport?

[manarak]

and the fact that pilots requested emergency vehicles before the crash

Is there a source for this detail? I haven't read/heard a mention of this request. Did the flight deck made this request well out from the airport?

yes, please check my earlier post:

http://www.thaivisa.com/forum/topic/651859-boeing-777-plane-crash-lands-at-san-francisco-airport/page-3#entry6586519

[rice555]

Not being a plot or any sort of aviation expert, I'd love to know why there is a 'sea wall' however low at the start/end of a runway?

for preventing planes that overshoot from falling into the sea

Well excuse my ignorance, but how would it be 'better' for a plane to hit a wall compared to skidding on into the sea?

Hello All, Khunken, the water at that end of the RR is not more than 8-12' depending on tides.

I worked on a JAL DC-8 that landed short, nobody hurt, cost $4mil to clean and OV, flew another

15 years.

Yes it was the same runway.

rice555

[Mudcrab]

This is actually a flight I've considered in the past as part of my return route home. Can't describe how goddamn scary that is!

Definitely pilot error.

R.I.P. to the flight crew that was lost out the rear. A terrifying day in aviation.

A pox on you! Wait for the results of the investigation before you start apportioning blame!

No chance of air traffic control, stuffing up

[SeaVisionBurma]

Unhelpful post removed

[Loptr]

Here is a picture of the plane just after crashing and before it was engulfed in flames.

http://www.theverge.com/2013/7/6/4499044/samsung-executive-david-eun-in-boeing-777-crash-most-everyone-seems-fine

Notice the people getting off carry hand luggage and how the front slide is not being used and the person possible in cockpit.

If you look at all pictures on CNN website you will not see any landing gear.

So my guess is as a humorous aside is that the pilot did not put down the landing gear.

Witnesses say it bounced and cart wheeled. Lets see what the investigators have to say.

I think though that the photo I have linked above is the best.

The gear came off on initial impact. You can see them in the debris field just at the runway threshold.

[TallGuyJohninBKK]

If I put together the comparison of the flight trajectories and the fact that pilots requested emergency vehicles before the crash, the pilot error becomes a less likely scenario. Still likely, but less so. They might also have been let down by the engines.

I was reading some discussion of a prior 777 crash where engine performance/fuel starvation due to ice crystals on descent was determined as the cause of the January 2008 crash prior to landing at London Heathrow of a BA flight. But the news indicates that the authorities subsequently mandated a fix for all impacted aircraft to be implemented by Jan 2011.

http://en.wikipedia.org/wiki/British_Airways_Flight_38

British Airways Flight 38 (call sign Speedbird 38) was a scheduled flight operated by a British Airways Boeing 777 from Beijing Capital International Airport which crash landed just short of the runway at its destination, London Heathrow Airport, on 17 January 2008 after an 8,100-kilometre (4,400 nmi; 5,000 mi) flight.^[1][2][3] There were no fatalities but 47 people sustained injuries; one serious.^[4] The 150-tonne aircraft was the first Boeing 777-200ER to be written off in the model's history,^[5][6] and the first hull loss of any Boeing 777.

Ice crystals in the fuel were the cause of the accident, clogging the fuel-oil heat exchanger (FOHE) of each engine. This restricted fuel flow to the engines when thrust was demanded during the final approach to Heathrow.^[7] Boeing identified the problem as specific to the Rolls-Royce engine fuel-oil heat exchangers, and Rolls-Royce has subsequently developed a modification to its FOHE; the European Aviation Safety Agency (EASA) mandated that all affected aircraft were to be fitted with the modification before 1 January 2011.^[4][8] Boeing 777 aircraft powered by GE or Pratt & Whitney engines were not affected by the problem.^[8]

[manarak]

If I put together the comparison of the flight trajectories and the fact that pilots requested emergency vehicles before the crash, the pilot error becomes a less likely scenario. Still likely, but less so. They might also have been let down by the engines.

I was reading some discussion of a prior 777 crash where engine performance/fuel starvation due to ice crystals on descent was determined as the cause of the January 2008 crash prior to landing at London Heathrow of a BA flight. But the news indicates that the authorities subsequently mandated a fix for all impacted aircraft to be implemented by Jan 2011.

http://en.wikipedia.org/wiki/British_Airways_Flight_38

British Airways Flight 38 (call sign Speedbird 38) was a scheduled flight operated by a British Airways Boeing 777 from Beijing Capital International Airport which crash landed just short of the runway at its destination, London Heathrow Airport, on 17 January 2008 after an 8,100-kilometre (4,400 nmi; 5,000 mi) flight.^[1][2][3] There were no fatalities but 47 people sustained injuries; one serious.^[4] The 150-tonne aircraft was the first Boeing 777-200ER to be written off in the model's history,^[5][6] and the first hull loss of any Boeing 777.

Ice crystals in the fuel were the cause of the accident, clogging the fuel-oil heat exchanger (FOHE) of each engine. This restricted fuel flow to the engines when thrust was demanded during the final approach to Heathrow.^[7] Boeing identified the problem as specific to the Rolls-Royce engine fuel-oil heat exchangers, and Rolls-Royce has subsequently developed a modification to its FOHE; the European Aviation Safety Agency (EASA) mandated that all affected aircraft were to be fitted with the modification before 1 January 2011.^[4][8] Boeing 777 aircraft powered by GE or Pratt & Whitney engines were not affected by the problem.^[8]

Well, yes.

But we cannot assume with 100% certainty that:

- the ice crystal problem is the only problem that could cause loss of engine power

- the fix was successful in removing all ice crystal related problems

- the fix has been correctly applied to the aircraft

So the fix of the earlier ice crystal problem may or may not be totally or partially unrelated to Asiana 214's crash.

If the flight recorders report loss of engine power or engines not responding normally to pilots' commands, technical failure is certain.

What seems strange to me is that plunge in the last segment visible on the trajectory. Since the pilots were manually landing the aircraft because of KSFO's shutting down the electronic landing system, I would not imagine a pilot of any experience level wanting to lose altitude so quickly for a landing, look at the angle, it just doesn't look credible that it was the result of an intentional manoeuver.

If they came in too low, the trajectory should have been much flatter towards the end, yet until just a segment before the runway they had sufficient height.

[manarak]

If I put together the comparison of the flight trajectories and the fact that pilots requested emergency vehicles before the crash, the pilot error becomes a less likely scenario. Still likely, but less so. They might also have been let down by the engines.

I was reading some discussion of a prior 777 crash where engine performance/fuel starvation due to ice crystals on descent was determined as the cause of the January 2008 crash prior to landing at London Heathrow of a BA flight. But the news indicates that the authorities subsequently mandated a fix for all impacted aircraft to be implemented by Jan 2011.

http://en.wikipedia.org/wiki/British_Airways_Flight_38

Boeing 777 aircraft powered by GE or Pratt & Whitney engines were not affected by the problem.^[8]

if you read what Boeing said in detail about that:

In the most recent note to operators, Boeing says that 777s powered by GE and Pratt & Whitney engines are not prone to the problem. "Based on our knowledge of the system configurations, scenario studies and laboratory test results, we do not believe that immediate action is necessary or warranted for 777s powered by other engine types or non-777 airframes regardless of engine type,"

this simply means that no problems were reported with the other engine types, while 2 or 3 problems were reported with the RR engines.

2 or 3 problems vs. 0, we are still well within statistical standard deviation for such a sample, and they "believe", "based on their knowledge", "no immediate action necessary" (is a non-immediate action necessary?). For an industry that very much relies on rocket science, I think the statement is very cautious.

So it could simply mean that a problem with the other engines simply hasn't yet occured.

[khaosai]

Hi,

Lots of speculation which is understandable, and normal behaviour for people to come up with some theories to what caused the crash.

Depth perception landing on water would be a challenge. This is slightly different where you have a long runway as your primary focus. Large aircraft don't use the threshold as an aiming point. What you use is the touchdown zone markings at the 300 metre point on the runway. When on profile you will cross the threshold at approx 50ft and commence the flare between 20 and 30ft on the B777.

A normal approach will generally have some sort of glide slope guidance, be it accurately using the instrument landing system, RNAV approach or perhaps an approach that gives you a height check against a certain distance from touchdown. This was a visual approach conducted in nice weather that has gone badly wrong during the final stages of the approach. The aircraft has hit the wall approx 500 metres prior to the required touchdown point. The aircraft is capable of conducting an auto land but needs the full instrument landing components to be completed safely. Recency for this type of approach is now generally conducted every 6 months in the simulator.

Jet engines from different manufacturers will have different spool up times from the idle position, the difference being whether they are 2 or 3 spool. This difference is only from the idle position. They normally get to the take off power setting around the same time.

Just trying to clear up some misconceptions from some of the above posts.

[manarak]

Hi,

Lots of speculation which is understandable, and normal behaviour for people to come up with some theories to what caused the crash.

Depth perception landing on water would be a challenge. This is slightly different where you have a long runway as your primary focus. Large aircraft don't use the threshold as an aiming point. What you use is the touchdown zone markings at the 300 metre point on the runway. When on profile you will cross the threshold at approx 50ft and commence the flare between 20 and 30ft on the B777.

A normal approach will generally have some sort of glide slope guidance, be it accurately using the instrument landing system, RNAV approach or perhaps an approach that gives you a height check against a certain distance from touchdown. This was a visual approach conducted in nice weather that has gone badly wrong during the final stages of the approach. The aircraft has hit the wall approx 500 metres prior to the required touchdown point. The aircraft is capable of conducting an auto land but needs the full instrument landing components to be completed safely. Recency for this type of approach is now generally conducted every 6 months in the simulator.

Jet engines from different manufacturers will have different spool up times from the idle position, the difference being whether they are 2 or 3 spool. This difference is only from the idle position. They normally get to the take off power setting around the same time.

Just trying to clear up some misconceptions from some of the above posts.

Hi, since you have profound understanding of the matter, could you please have a look at the measurement points in flight 214's final approach here:

https://twitter.com/sbaker/status/353611787750494208/photo/1

and give your personal speculation about why the descent was so steep in the last segment?

[pomchop]

On March 3, 2001 I was waiting to board a Thai airways flight from Don Muang to Chiang Mai. Boarding was delayed a few minutes for some unknown reason. Then as I stood near the front of the boarding line the plane exploded at the gate. A massive fireball bounced off the very strong windows at the gate and the plane burned to a crisp and broke in half.

Within a few minutes it was all over the news that then PM Taksin was to be on board and the reason the boarding had been delayed was he was stuck in traffic and they were waiting for his arrival.Almost immediately the news was reporting that it was an assassination attempt on Taksin and a bomb had been planted on the plane. Nearly everyone seemed to believe this was the obvious cause.

But over the coming days/weeks as Boeing and the NSTB sent in teams to investigate the explosion they determined that it was NOT a bomb but an electrical short that set off some fumes near the fuel tank. Even then many refused to believe it and thought that Boeing was involved in some giant conspiracy to cover up the "real reason" that the plane exploded. As if Boeing would somehow prefer that the explosion was a mechanical issue for which they could be held liable rather than a bomb?

So in a strange twist of fate to this day myself and about one hundred other passengers that day can "thank" Taksin for being late for his flight. Otherwise we would have all been toast. Two of the cabin crew died in the explosion that day.

So I guess overall it is better not to be too quick to jump to conclusions as sometimes things are not quite what they seem.

[khaosai]

Hi,

Unstable approaches are a huge threat to the industry. Most airlines have a published stabilisation criteria. Speed, descent rate, power setting etc.

This approach at max landing weight would have required a descent rate of approx 700ft per minute. If you have started off high then it's a challenge as time is compressed the closer you get to the runway. Boeing commonly refer to the safest course of action in their documentation, so possibly in this case a go around would have been a more appropriate decision to make.

I would rather comment on digital flight data information than the info you have provided, however it could well give some clues to the end result.

[theajarn]

*Snipped*

. All of this points to pilot error, but of course the NTSB will not jump to conclusions and will perform their due diligence before blaming the pilot.

Unlike so many posters on Thaivisa.

Pilot error too early. Didn't triple 7 come up short in London due to a fuel issue on final approach. Could have been a fuel issue causing slow throttle response.

Micro burst??? Was there any weather in the area? They would already know if a microburst and would have had a LLWAS. They have pretty decent low level wind shear warning systems since the 1985ish Delta L1011 incident in Dallas.

Was that the one due to the icing problem

? All 777s were SUPPOSED to have that problem fixed, Boeing sent out an order to have them all fixed by a certain date (which I think has already passed).

[ableguy]

This is actually a flight I've considered in the past as part of my return route home. Can't describe how goddamn scary that is!

Definitely pilot error.

R.I.P. to the flight crew that was lost out the rear. A terrifying day in aviation.

A pox on you! Wait for the results of the investigation before you start apportioning blame!

As an ex pilot I could come up with various possabilities but it would be just speculation, I can assure you th NTSB do not indulge in speculation, just wait for the real cause to be known

[negreanu]

This approach at max landing weight would have required a descent rate of approx 700ft per minute. If you have started off high then it's a challenge as time is compressed the closer you get to the runway. Boeing commonly refer to the safest course of action in their documentation, so possibly in this case a go around would have been a more appropriate decision to make.

Dude they just flew from incheon to San Fran. Its no where near max landing weight

[NomadJoe]

This is actually a flight I've considered in the past as part of my return route home. Can't describe how goddamn scary that is!

Definitely pilot error.

R.I.P. to the flight crew that was lost out the rear. A terrifying day in aviation.

I've landed at that airport many times. It is a bit scary landing on what looks like water till the last second.

[khaosai]

Hi,

Fair comment regarding weight, truth be told I don't know what the actual weight was. It was more of an idea of approach speeds versus rate of descent. Lets assume it was 30 tons lighter then. Approx 10kts less speed on approach the required descent rate would be in the region of 650ft per minute.

It's not however uncommon to fly long distances on large aircraft and land at or close to max landing weight.

[Farangdam]

the pilot is alive....so he can tell the truth on what is going on....+ the plane looks like not totaly destroyed... this going to be a fast conclusion Rip and those are injured may get well as soonest..

[TallGuyJohninBKK]

I haven't seen a clear answer on whether the engines on this crash aircraft were made by P&W or RR (I gather both companies provide engines for various 777ERs)... And the Asiana CEO said at their news conference that they had no indication of engine failure on the plane.

But curiously, there was a story on the BBC just the other day about issues over RR's engine quality practices.

http://www.bbc.co.uk/news/business-23192857

5 July 2013 Last updated at 03:43 GMT

Rolls-Royce defends claims it concealed engine defects

Rolls-Royce has denied claims made by two former employees in a US lawsuit that it "cut corners on quality control requirements" and "lied to" customers.

The pair also alleged that the firm "routinely used defective parts designated as 'scrap only'".

The two are challenging a court order that prevents them from releasing information which they claim reveals details of what the firm concealed.

Rolls-Royce has defended itself and said the lawsuit is "without merit".

According to reports in the Financial Times and the Daily Telegraph, the lawsuit filed by former employees Thomas McArtor and Keith Ramsey alleges that the engine maker concealed internal records of defects in engines sold to clients.

The employees claims that the company collated those alleged defects into a "secret set of books"

http://www.bbc.co.uk/news/business-23192857

[geriatrickid]

To put this in perspective, China State media has identified the two fatalities as 16 year old middle school girls. Someone's kids.

There was a high school class trip of 20+ students on the plane. The girls were found outside the plane.

As the convoluted theories as to the cause of the crash are put forward, perhaps a kind thought can be spared for those kids. Of the 10 patients still in serious condition, 2 are children.

On the positive side, the SFO response was topnotch with a rapid emergency service turnout and a fantastic performance by the medical teams at the hospitals. The plane held up, the evacuation procedures worked and despite the chaos, the SFO catastrophe response performed as it was intended with all the drills and planning paying off. I am a long time admirer of the B777 and of the SFO airport and rather than this putting me off flying, it reassures me. If a crash was going to happen, this was one of the better airports for it have occurred at.

[manarak]

To put this in perspective, China State media has identified the two fatalities as 16 year old middle school girls. Someone's kids.

There was a high school class trip of 20+ students on the plane. The girls were found outside the plane.

As the convoluted theories as to the cause of the crash are put forward, perhaps a kind thought can be spared for those kids. Of the 10 patients still in serious condition, 2 are children.

On the positive side, the SFO response was topnotch with a rapid emergency service turnout and a fantastic performance by the medical teams at the hospitals. The plane held up, the evacuation procedures worked and despite the chaos, the SFO catastrophe response performed as it was intended with all the drills and planning paying off. I am a long time admirer of the B777 and of the SFO airport and rather than this putting me off flying, it reassures me. If a crash was going to happen, this was one of the better airports for it have occurred at.

true, but would it have happened at all if they didn't switch off their ILS?

(not implying a fault)

[TallGuyJohninBKK]

The latest news reports say the black box devices from the aircraft, both the voice cockpit recordings and the aircraft operational data tracking, have been recovered and are already in Washington DC for analysis.

Re GK's rosey perspective above, I'll say that SF certainly does have some large and good hospitals, fortunately for those injured... And I suspect the aircraft crew deserve credit for helping evacuate the plane as quickly as occurred.

But in terms of the emergency response activity at the time of the crash, from the various reports I've read, it seems that many on the plane had already been evacuated down the emergency chutes by the time most of the emergency response units arrived.

As CNN noted:

Perhaps one of the reasons so many people survived Saturday's crash was because the Boeing 777 is built so that everybody can get off the plane within 90 seconds, even if half the doors are inoperable.

BTW, I was just reading the Sunday morning U.S. news accounts of the crash.... And the NY Times piece makes almost no mention of any potential crash contributing factors, including the ILS issue...nor do the various Associated Press reports I've read.

The latest Reuters report includes the following brief snippet:

A San Francisco airport spokesman said that a component of the facility's instrument landing system that tracks an incoming airplane's glide path was not working on Saturday.

Pilots and air safety experts said the glide path technology was far from essential for a safe landing in good weather.

http://www.reuters.com/article/2013/07/07/us-usa-crash-asiana-idUSBRE9650E220130707

[Tywais]

Pilots and air safety experts said the glide path technology was far from essential for a safe landing in good weather.

To clarify this. It is not uncommon for commercial airliners to not use ILS when under VFR (Visual Flight Rules) conditions and fly by VFR rules. Some places may require to have ILS turned on but not necessary to use IFR rules unless required by weather conditions or at the request of control. So ILS is not at all necessary in good weather conditions.

There are alternate glide slope indicators at nearly all airports referred to as a VASI system (Visual Approach Slope Indicator) or variations of it such as PAPI (Precision Approach Path Indicator which SFO has) or PVASI (Pulsating VASI). These are all visual, non electronic, means of flying the final approach glide slope. There are two light, 3 light and 4 light systems - PAPI using 4 lights. Note the 4 lights to the left. SFO has a 4 light PAPI on the left side of the runways.

I remember the last training flight before taking my flight exam for my license. It was a night flight and the instructor put me under 'the hood' to simulate instrument flight conditions in that I could not see outside and only use the instrument panel. We spent an hour doing flight procedures and maneuvers under instrument conditions. When it was time to return to the field my instructor requested that I do an instrument landing. This means contacting the approach control tower and request radar vectoring to landing. That means the tower will give me full instructions such as turning to heading, altitude, descent rate and airspeed and guide me back to the runway using only the instruments and the approach control instructions.

They guided me directly on path and announced my height foot by foot. When the instructor had me remove the hood I was just crossing the threshold and at flare out height, just a few feet above runway. He wanted me to do the complete landing including touch down without even seeing the runway but exhaustion was too much. I stepped out of the plane pleased with myself but also felt like I had just ran a marathon. Shaky and sweaty.

[TallGuyJohninBKK]

I'm not a pilot or especially well versed in aviation things...

But, some of the same news reports I've read over the past day that talked about the FAA notice re SFO's ILS being down for a couple months also talked about some backup system, and I want to recall it was a name like the VASI or PAPI, had been working only intermittently.

I see one of the Fox affiliates has this following excerpt in their coverage:

Airport technology called the Instrument Landing System, or ILS — which normally would help pilots correctly approach the runway — was not operating at the time, according to a Federal Aviation Administration bulletin.

“There are a lot of systems that help support pilots” as they fly into busy airports, Hersman [from the NTSB] said. Some of these systems alert the pilots. “A lot of this is not necessarily about the plane telling them” that something may be wrong, she said. “It’s also about the pilot’s recognition of the circumstances and what’s going on. So for them to be able to assess what’s happening and make the right inputs to make sure they’re in a safe situation — that’s what we expect from pilots.”

The ILS integrates with the aircraft’s cockpit to trigger a audible warning, retired 777 pilot Mark Weiss told CNN. “You hear a mechanical voice that says, ‘too low, too low, too low.’” The ILS is “nice to have,” Weiss said, “but it’s not critical on the 777.” There are redundant systems aboard the aircraft that would provide similar warnings if the plane was coming in too low, said Weiss, who has landed 777s hundreds of times.

Weiss said he’s perplexed by the details surrounding the crash landing. If the pilot was somehow unaware the plane was coming in too low, Weiss wonders why another member of the flight crew didn’t speak up and warn him.

http://fox40.com/2013/07/07/flight-data-recorders-recovered-from-asiana-crash/#ixzz2YNxg2EJ8

Ya, I happened to be watching Fox News on TV Sunday morning and caught their reporting on the crash....and summarized their account in post #36 here in this thread:

But FWIW, Fox News U.S. was reporting this morning that the ILS (Instrument Landing System) system at SFO was down at the time of the crash, and had been scheduled to be down for a two-month period, and that some other kind of colored lighting system on the runway designed to assist pilots when the ILS was out had only been working intermittently.

[TallGuyJohninBKK]

I see Fox News network's latest report has a somewhat fuller discussion of the ILS issue, including a reference to it in the lead of their latest report. Here's the pertinent excerpt.

Authorities are also looking into what role the shutdown of glide slope -- a pilot navigational aid -- had in the crash.

Hersman said on CBS' "Face the Nation" that the system is a ground-based aid that helps pilots stay on course while landing and it has been shut down since June. The pilots, however, were notified before the crash that the system wasn't available.

Aircraft security experts told Reuters that the glide slope system is not essential for routine landings, but it's not unusual for airports to disable them for maintenance reasons.

"The pilots would have had to rely solely on visual cues to fly the proper glide path to the runway, and not have had available to them the electronic information that they typically have even in good weather at most major airports," said Captain Chesley "Sully" Sullenberger, who crash landed a plane in New York's Hudson River in 2009, told a CBS news affiliate, according to Reuters.

"What that means is that then the automatic warnings that would occur in the cockpit when you deviate below the desired electronic path wouldn't have been available either. So we don't know yet if that's a factor in this particular situation, but that's certainly something they'll be looking at," he said.

http://www.foxnews.com/us/2013/07/07/boeing-777-crashes-at-san-francisco-international-airport/#ixzz2YO0Nwqdd

[Tywais]

Ya, I happened to be watching Fox News on TV Sunday morning and caught their reporting on the crash....and summarized their account in post #36 here in this thread:

But FWIW, Fox News U.S. was reporting this morning that the ILS (Instrument Landing System) system at SFO was down at the time of the crash, and had been scheduled to be down for a two-month period, and that some other kind of colored lighting system on the runway designed to assist pilots when the ILS was out had only been working intermittently.

The PAPI is the colored lighting system they are referring to. Find it difficult to believe that it would be working intermittently as it is a static piece of equipment and not sophisticated electronics at all. Also they would have a GPWS (Ground Proximity Warning System ) in the aircraft which uses a radar altimeter to give them precise height above ground information and can supply automated voice proximity warnings. There are other methods such as using distance to the field and descent information that will give you glide slope information. Lots of ways to safely land the aircraft without the use of ILS.

a Ground proximity warning system (GPWS), or Ground collision warning system (GCWS), which uses a radar altimeter to detect proximity to the ground or unusual descent rates. GPWS is common on civil airliners and larger general aviation aircraft.